# The effects of superheating and cooling rate on olivine growth in chondritic liquid

Marion Auxerre, François Faure, Delphine Lequin

► To cite this version:

Marion Auxerre, François Faure, Delphine Lequin. The effects of superheating and cooling rate on olivine growth in chondritic liquid. Meteoritics and Planetary Science, 2022, 57, pp.1474-1495. 10.1111/maps.13830. insu-03777749

HAL Id: insu-03777749

https://insu.hal.science/insu-03777749v1

Submitted on 20 Aug 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# The effects of superheating and cooling rate on olivine growth in chondritic liquid

Marion AUXERRE ID*, François FAURE, and Delphine LEQUIN

Centre de Recherches Pétrographiques et Géochimiques, UMR 7358, CNRS and Université de Lorraine, Nancy 54500, France

*Corresponding author. E-mail: marion.auxerre@univ-lorraine.fr

*(Received 27 July 2022; revision accepted 25 April 2022)

**Abstract**—Chondrules, the major constituent of chondrites, are millimeter-sized igneous objects resulting from the crystallization of silicate liquids produced by the partial or complete melting of chondritic precursors, whose exact nature remains disputed. Various chondrule textures are observed as a function of the extent of the initial melting event. Here, we report dynamic crystallization experiments performed with a broad range of cooling rates (2–750 °C h⁻¹) from superliquidus or subliquidus initial conditions to demonstrate the control of nucleation on the final chondrule texture. Classical cryptorphyritic, micro-porphyritic, and porphyritic olivine textures were reproduced in subliquidus experiments in which heterogeneous nucleation dominates. In contrast, we were unable to reproduce barred olivine textures, regardless of the cooling rates investigated from superliquidus conditions; instead, macro-porphyritic textures were systematically obtained at low cooling rates (<10 °C h⁻¹). The small number and large size of crystals in the macroporphyritic texture are consistent with the initial step of superheating and the presence of long embayments that indicate an initial episode of rapid growth due to delayed nucleation. Crystals then acquired polyhedral shapes during a subsequent episode of slow growth. When the growth rate is too slow to decrease the degree of supersaturation in the liquid, a new episode of rapid growth produces a new generation of melt inclusions.

## INTRODUCTION

Chondrites are among the first rocks formed in the solar system (Burkhardt et al., 2012; Connelly et al., 2012; Ivanova, 2016; McSween & Huss, 2010). They comprise refractory inclusions (CAIs, Ca-Al-rich inclusions; and AOAs, amoeboid olivine aggregates) and chondrules embedded in a matrix that may contain large, isolated olivine crystals. Chondrules, the main constituents of chondrites (>80% of ordinary chondrites; Scott & Krot, 2014), are igneous spherules a few millimeters in diameter (Grossman et al., 1988) that result from the crystallization of precursors that experienced various degrees of melting. However, this crystallization scenario is probably too simplistic: Chondrules commonly show radially zoned silica concentrations that are often associated with important sodium concentrations, suggesting that chondrules evolved in open-system exchange with the nebular gas (Barosch et al., 2019; Jacquet et al., 2012; Libourel et al., 2006; Marrocchi et al., 2018; Tissandier et al., 2002)

and not in a closed system as initially proposed in the “dustball” model requiring flash heating to prevent the evaporation of sodium (Grossman et al., 1988; Hewins, 1991; Jones, 1994).

Chondrules are grouped according to their texture and chemical composition (Gooding & Keil, 1981). Most chondrules (>80% in ordinary chondrites; Grossman et al., 1988) are porphyritic, containing euhedral and polyhedral crystals of olivine and pyroxene set in a fine-grained or glassy mesostasis (Lofgren, 1989). According to the relative abundances of olivine and pyroxene, porphyritic chondrules are classified as porphyritic olivine pyroxene (POP, roughly equivalent abundances of olivine and pyroxene), porphyritic olivine (PO, more olivine than pyroxene), or porphyritic pyroxene chondrules (PP, mostly pyroxene; Gooding & Keil, 1981). However, a recent study demonstrated that the classification with relative abundances of olivine and pyroxene is probably due to the sectioning effects of porphyritic chondrules (Barosch et al., 2020). As a function of crystal size, porphyritic textures are defined
as micro-porphyritic (crystals smaller than 200 µm), macro-porphyritic (crystals larger than 500 µm), or porphyritic stricto sensu for intermediate sizes (Jones, 1992). Nonporphyritic chondrules are also present in chondrites, including barred olivine (BO; dendritic parallel bars of olivine), radial pyroxene (RP; fine, dendritic, fan-shaped pyroxene crystals), granular olivine (GO; many subhedral crystals smaller than 10 µm), and cryptocrystalline chondrules (CC; comprising glass and very small, sometimes dendritic crystals; Connolly & Hewins, 1995; Donaldson, 1976; Gooding & Keil, 1981; Lauretta et al., 2006).

According to their chemical composition, particularly the FeO contents of olivine and pyroxene crystals, chondrules are characterized as type I when the fayalite content of olivine (Fa, the iron endmember of the olivine solid solution) and/or the ferrosilite content of pyroxene (Fs, the iron endmember of the pyroxene mineral series) are <10 mol or as type II when Fa and/or Fs exceed 10 mol (McSween, 1977). Although type I chondrules contain iron-nickel metal balls indicating that they are more reduced than type II chondrules, both chondrule types show similar textures. In contrast, crystals in type II porphyritic chondrules are often larger (0.75-0.95 mm) than those in type I chondrules (0.6 mm; Jones et al., 2018; Sears et al., 1996). Regardless of their composition and texture, olivine crystals usually display macroscopic defects such as glass inclusions or embayments (Faure et al., 2012; Varela et al., 2002, 2006). Therefore, whether an open- or closed-system model is invoked to explain crystal compositions, the principal mechanisms controlling the morphology of the crystals and their associated macroscopic defects are nucleation and growth.

Experimental studies have shown that the final chondrule texture is essentially controlled by crystal nucleation (Lofgren & Russell, 1986).

The principal parameter controlling chondrule texture is the maximum (peak) temperature to which the silicate liquid was initially heated before cooling and crystallization. If the silicate liquid is superheated, that is, heated above its liquidus temperature, fewer crystals form during cooling. Nonporphyritic textures (except GO) are explained by superheating, which acted to diminish or totally eliminate crystal nuclei within the silicate liquid (Hewins, 1983, 1989; Lofgren, 1989). In contrast, experiments with subliquidus initial temperatures show numerous crystals analogous to porphyritic textures after cooling because crystal nuclei or relict crystals are maintained in the silicate liquid (Lofgren, 1989). Thus, the number and size of crystals are a function of the starting temperature, which controls the nucleation rate.

In superheated silicate liquids, the time spent at superliquidus temperatures can also influence the final chondrule texture (Donaldson, 1979; First et al., 2020). This parameter is important because porphyritic textures can be reproduced even after an initial superheating step if the duration of superheating is short enough to preserve nuclei or relict crystals (Connolly et al., 1998).

Finally, cooling rate also exerts an important control on the final observed texture. In experiments with superliquidus initial temperatures, olivines crystallized at slow cooling rates (<50 °C h⁻¹) are euhedral or polyhedral whereas those crystallized at faster cooling rates (>50 °C h⁻¹) are skeletal or dendritic (Faure, Trolliard, Nicollet, et al., 2003; Lofgren, 1989). In contrast, experiments performed with a starting temperature slightly below the liquidus produce euhedral phenocrysts over a large range of cooling rates (5–100 °C h⁻¹), and extremely fast cooling rates (>1000 °C h⁻¹) are necessary to crystallize skeletal olivine (Lofgren, 1989; Tsuchiyama & Nagahara, 1981).

Therefore, crystal textures in both extraterrestrial and magmatic rocks (Lofgren, 1983) are conditioned by the initial nucleation step, which is controlled by the initial temperature relative to the liquidus, the duration of superheating (if it occurred), and kinetics.

In this experimental study, we examine the influence of the starting temperature on the resulting textures after slow cooling (2 °C h⁻¹). We explore a large range of superliquidus and subliquidus initial temperatures. Our results confirm that a sharp textural boundary exists between experiments cooled from above or below their liquidus temperatures. Moreover, we show that cooling rate has an impact on crystal abundance (i.e., nucleation), even if the effect of cooling rate is less evident than that of starting temperature in the final texture. Above all, we focus on the formation of melt inclusions in relation to supersaturation due to delayed nucleation or inhomogeneous crystal distributions in the experimental charges.

## EXPERIMENTAL PROTOCOL

Four starting compositions (Table 1) were prepared from mixtures of reagent grade oxides, melted above their liquidus temperatures for 6 h in a platinum crucible, and quenched in water. The resulting glasses were ground to a fine powder with ethanol in an automatic grinder. This melting and grinding protocol was performed twice to ensure the homogeneity of the starting glass powders. Two compositions (Fo#18 and Fo#19) were initially used to demonstrate that glass inclusions hosted in magnesian olivine within PO chondrules are indeed melt inclusions (Faure
<table><caption>Table 1. Starting bulk compositions used in this study (Fo#18-19-23-24; wt%, errors reported in parentheses) and their associated liquidus ($T_{liq}$) compared to starting bulk composition.</caption><thead><tr><th></th><th>Fo#18</th><th>Fo#19</th><th>Fo#23</th><th>Fo#24</th><th>PO47 (1)</th><th>51 (2)</th></tr></thead><tbody><tr><td>$T_{liq}$ (°C)*</td><td>1603</td><td>1536</td><td>1341</td><td>1561</td><td>1510</td><td>1525</td></tr><tr><td>SiO<sub>2</sub></td><td>44.62 (0.06)</td><td>47.32 (0.36)</td><td>49.03 (0.12)</td><td>50.69 (0.17)</td><td>56.84 (0.67)</td><td>40.12 (0.25)</td></tr><tr><td>MgO</td><td>33.85 (0.13)</td><td>28.48 (0.46)</td><td>17.23 (0.09)</td><td>32.16 (0.13)</td><td>28.79 (0.64)</td><td>45.61 (0.68)</td></tr><tr><td>Al<sub>2</sub>O<sub>3</sub></td><td>12.04 (0.15)</td><td>11.96 (0.07)</td><td>13.26 (0.09)</td><td>11.20 (0.12)</td><td>3.71 (0.83)</td><td></td></tr><tr><td>CaO</td><td>9.46 (0.10)</td><td>12.21 (0.22)</td><td>20.47 (0.14)</td><td>5.92 (0.05)</td><td>1.68 (0.20)</td><td>0.07 (0.001)</td></tr><tr><td>FeO</td><td></td><td></td><td></td><td></td><td>8.99 (0.79)</td><td>14.20 (0.33)</td></tr><tr><td>Total</td><td>100</td><td>100</td><td>100</td><td>100</td><td>100</td><td>100</td></tr></tbody></table>

*Liquidus temperatures for Fo#18 and Fo#19 were experimentally determined herein (see Fig. 1a and Experimental Protocol section).

1—Lofgren and Russell (1986); 2—Jones and Lofgren (1993).

et al., 2012). In the other two compositions (Fo#23 and Fo#24), we increased the range of MgO (and thus the liquidus temperatures) and CaO contents investigated. All starting compositions were chosen to be in the forsterite stability field. Only one composition (Fo#24) should crystallize Ca-poor pyroxene as a secondary phase, and all other starting compositions should crystallize plagioclase. However, because the starting temperatures used to nucleate olivine were well above the pyroxene and plagioclase liquidus, these secondary phases failed to nucleate (Faure, 2020; Faure et al., 2012). It is important to note that four compositions used in our experiments were richer in Al and Ca than bulk chondrules (Table 1); however, these compositions may be representative of chondrule melts containing abundant CAIs or AOAs before interaction with the Mg-Si-rich gas.

The starting glass powders were formed into pellets and placed on a platinum wire loop at the end of an alumina rod positioned in the hot spot of Nabertherm vertical tube furnace. A thermocouple within the alumina rod, calibrated against the melting points of gold and palladium, was positioned within 1 cm of the sample pellets.

Three thermal protocols were used (Fig. 1; detailed in the following paragraphs), and all experiments have undergone a 1 h dwell at starting temperature and were quenched in water.

The first protocol (Fig. 1a) corresponds to isothermal experiments in which the charges were held for 1 h at a constant temperature before quenching. The temperature was varied across different experiments to determine the liquidus temperatures ($T_{liq}$) of compositions Fo#23 and Fo#24 (Table 1). The liquidus temperatures of starting glasses Fo#18 and Fo#19 were experimentally determined by Faure et al. (2012).

The second protocol (Fig. 1b) corresponds to dynamic crystallization experiments. Charges were first heated to various superliquidus or subliquidus temperatures for 1 h,

that is, the degree of superheating is defined as $+\Delta T = T$ starting experiment – T liquidus and the degree of underheating is defined as $-\Delta T_s = T$ starting temperature – T liquidus. Then, charges were cooled to 1200 °C at a constant rate of 2 °C h⁻¹ and quenched.

The third protocol (Fig. 1c) was only performed with the Fo#24 starting composition. Charges were initially heated to the same degree of superheating (+ΔT = 10 °C), but were then cooled to 1200 °C at various rates ranging from 2 to 700 °C h⁻¹ before quenching.

After quenching, charges were mounted in epoxy and prepared as polished sections. The charges were polished in the plane of the platinum wire in order to have a sufficiently large surface area (ideally ~7 mm²) to quantify the crystal assemblages; the exact surface area analyzed for each charge is reported in Table 2. Polished sections were examined under a petrographic microscope using transmitted, plane-polarized light, and by scanning electron microscopy (SEM) using a JEOL 6510 equipped with a Bruker XFlash-type energy-dispersive spectroscopy (EDS) system at the Centre de Recherches Pétrographiques et Géochimiques (CRPG, Nancy, France). Chemical characterization by EDS was performed using an accelerating voltage of 15 keV, on-peak counting times of 10–20 s, and a focused beam. We used two methods to determine the number of crystals within the charges. The number of crystals in initially superheated charges was quantified with depth in the charge with a petrographic microscope using transmitted, plane-polarized light. The number of crystals present at the polished surface of initially underheated charges was quantified by both SEM and with a petrographic microscope using reflecting light. Although these two quantification methods are not equivalent (the numbers of crystals in subliquidus experiments are underestimated compared to those in superliquidus experiments), we consider them a good approximation because the crystal abundances in the
<figure><img src="image_2.png" /><figcaption>Fig. 1. Schematic sketches of the three thermal protocols employed. a) Isothermal experiments performed at various superliquidus (+ΔT) or subliquidus temperature (−ΔT_s); b) dynamic crystallization experiments held for a fixed duration (i.e., 1 h) at either superliquidus or subliquidus temperature then cooled at a slow, constant rate of 2 °C h⁻¹; and c) dynamic crystallization experiments cooled at various cooling rates (CR) after being held for a fixed duration (i.e., 1 h) at constant superliquidus temperature of +ΔT = 10 °C. Each experiment was quenched in water (qch). (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

final charges generally differ by more than two orders of magnitude between the two types of experiments.

## RESULTS

### Slow Cooling Experiments (2 °C h⁻¹)

#### Superliquidus Experiments

Regardless of the chemical composition of the starting glass, all charges that were superheated before cooling show very few (none to six; Table 2) euhedral or polyhedral olivine crystals (Figs. 2 and 3). The chemical compositions of olivines (pure forsterite) and associated liquids are presented in Table S1 in supporting information. Importantly, regardless of the starting composition, olivines are of similar size: 1.2–2.8 mm long and 600 µm to 1.6 mm wide. Sometimes, a few smaller euhedral crystals (460–480 µm) are present in a small area of glass between the platinum wires (e.g., Fo#18, +ΔT = 8 °C; Fo#24, +ΔT = 50 °C). In addition, a few skeletal crystals are present near the platinum wire (Fig. 2; e.g., Fo#19, +ΔT = 25 °C; Fo#24, +ΔT = 0 and 10 °C); these crystals measure 300–700 µm long and are preferentially elongated along the [100] direction. Moreover, only the terminal tips of these crystals display hopper cavities characteristic of skeletal morphologies, indicating that the majority of the crystals' lengths are tabular in shape. Furthermore, in some charges (e.g., Fo#18, +ΔT = 8 °C; Fo#19, +ΔT = 75 °C; Fo#24, +ΔT = 50 °C), polyhedral olivine crystals display dendritic overgrowths 100–200 µm thick (Fig. 3a and 3b). We emphasize that liquidus experiments (e.g., Fo#24, for +ΔT = 0 °C) show results similar to superheating experiments, the exception being experiments with very high degrees of superheating (+ΔT > 226 °C, only possible with starting composition Fo#23 as it has the lowest liquidus temperature), which are totally glassy.

Large polyhedral olivine crystals frequently display melt inclusions and embayments, that is, incipient glass inclusions still connected to the external melt. Melt inclusions are rounded 15–30 µm in diameter, and sometimes contain shrinkage bubbles 3–10 µm in diameter (Fig. 3). Embayments are variably sized and shaped, but never contain shrinkage bubbles. Several embayments (three or four) can occur in the same crystal and are always elongated in the same direction (Fig. 4). We distinguish among three types of embayments. The first are long (e.g., 300–700 µm), winding (one to three turns), and narrow (e.g., 15–30 µm wide) necks of melt through the crystals, widening (e.g., to 150 µm) at the edge of their host crystals to form “estuaries” (Fig. 3). Embayments of the second type are smaller (15–25 µm long, Fig. 3) and always located along and elongated parallel to their host crystals’ rims. In some cases, embayments associated with dendritic overgrowths (Fig. 3b) are much wider. It is important to note that small, elongated glass inclusions near crystal rims could correspond to sectioned embayments, and we cannot conclusively determine whether they are true glass inclusions or remained connected to the external melt in the third dimension (Fig. 3b and 3c). Nonetheless, these inclusions are generally elongated parallel to the crystal faces and never show shrinkage bubbles, suggesting that they correspond to small embayments.

The third type of embayments, “complex embayments,” are only observed in charge Fo#24 superheated to +ΔT = 50 °C (Fig. 4). These embayments are not connected to the external melt. Although apparently closed in cross section, they do not show shrinkage bubbles, in contrast to nearby true glass inclusions (~40 µm diameter) containing shrinkage bubbles (<10 µm diameter). Therefore, this observation suggests that complex embayments remained connected with the external silicate liquid in the third dimension.
<table><caption>Table 2. Numbers and sizes of crystals in the charges cooled at 2 °C h⁻¹ from various initial thermal conditions.</caption><thead><tr><th>Composition</th><th>T<sub>liq</sub> (°C)</th><th>Run no.</th><th>ΔT* (°C)</th><th>S<sub>charge</sub> (mm²)</th><th>Nb cx</th><th>Nb<sub>n</sub> cx</th><th>L (mm)</th></tr></thead><tbody><tr><td rowspan="8">Fo#18</td><td rowspan="8">1603</td><td>N1-380</td><td>+8</td><td>4.5</td><td>3(1)</td><td>3</td><td>2.5 ± 1</td></tr><tr><td>N1-410</td><td>-10</td><td>3.9</td><td>94</td><td>121</td><td>0.320 ± 0.16</td></tr><tr><td>N1-421</td><td>-20</td><td>4.5</td><td>120</td><td>133</td><td>0.230 ± 0.11</td></tr><tr><td>N1-382</td><td>-32</td><td>6.3</td><td>200</td><td>159</td><td>0.130 ± 0.07</td></tr><tr><td>N1-407</td><td>-42</td><td>3.5</td><td>270</td><td>386</td><td>0.104 ± 0.04</td></tr><tr><td>N1-406</td><td>-52</td><td>4.4</td><td>310</td><td>352</td><td>0.1 ± 0.06</td></tr><tr><td>N1-449</td><td>-60</td><td>2.9</td><td>300</td><td>505</td><td>0.07 ± 0.06</td></tr><tr><td>N1-459</td><td>-203</td><td>4.2</td><td>1000</td><td>1190</td><td>0.02 ± 0.01</td></tr><tr><td rowspan="8">Fo#24</td><td rowspan="8">1561</td><td>N1-380</td><td>+50</td><td>4.5</td><td>2(1)</td><td>4</td><td>2 ± 0.2</td></tr><tr><td>N1-382</td><td>+10</td><td>3.5</td><td>3(2)</td><td>3</td><td>2 ± 1</td></tr><tr><td>N1-407</td><td>0</td><td>4</td><td>2(1)</td><td>3</td><td>2 ± 1.1</td></tr><tr><td>N1-406</td><td>-10</td><td>3.2</td><td>25</td><td>39</td><td>0.350 ± 0.09</td></tr><tr><td>N1-408</td><td>-35</td><td>4.4</td><td>180</td><td>205</td><td>0.130 ± 0.09</td></tr><tr><td>N1-409</td><td>-45</td><td>4.8</td><td>550</td><td>573</td><td>0.096 ± 0.09</td></tr><tr><td>N1-455</td><td>-55</td><td>4.8</td><td>650</td><td>677</td><td>0.08 ± 0.06</td></tr><tr><td>N1-456</td><td>-60</td><td>6.4</td><td>550</td><td>430</td><td>0.066 ± 0.06</td></tr><tr><td rowspan="8">Fo#19</td><td rowspan="8">1536</td><td>N1-457</td><td>-70</td><td>4</td><td>713</td><td>891</td><td>0.07 ± 0.06</td></tr><tr><td>N1-380</td><td>+75</td><td>6.5</td><td>2</td><td>2</td><td>1.2 ± 0.5</td></tr><tr><td>N1-382</td><td>+35</td><td>3.5</td><td>3</td><td>6</td><td>1.1 ± 0.01</td></tr><tr><td>N1-407</td><td>+25</td><td>6.5</td><td>3(1)</td><td>2</td><td>1 ± 0.1</td></tr><tr><td>N1-406</td><td>+15</td><td>4.3</td><td>2</td><td>2</td><td>1.2 ± 0.1</td></tr><tr><td>N1-408</td><td>-10</td><td>2.8</td><td>140</td><td>250</td><td>0.12 ± 0.08</td></tr><tr><td>N1-409</td><td>-20</td><td>4.8</td><td>550</td><td>573</td><td>0.13 ± 0.07</td></tr><tr><td>N1-451</td><td>-30</td><td>2.3</td><td>420</td><td>913</td><td>0.120 ± 0.09</td></tr><tr><td rowspan="8">Fo#23</td><td rowspan="8">1325</td><td>N1-452</td><td>-40</td><td>2.5</td><td>340</td><td>680</td><td>0.190 ± 0.09</td></tr><tr><td>N1-450</td><td>-50</td><td>2.1</td><td>230</td><td>542</td><td>0.210 ± 0.08</td></tr><tr><td>N1-459</td><td>-136</td><td>3.4</td><td>2800</td><td>4118</td><td>0.02 ± 0.01</td></tr><tr><td>N1-380</td><td>+270</td><td>4.8</td><td>0</td><td>0</td><td>—</td></tr><tr><td>N1-382</td><td>+230</td><td>4.7</td><td>0</td><td>0</td><td>—</td></tr><tr><td>N1-407</td><td>+220</td><td>4.7</td><td>0</td><td>0</td><td>—</td></tr><tr><td>N1-406</td><td>+210</td><td>5.4</td><td>2</td><td>2</td><td>1.5 ± 0.7</td></tr><tr><td>N1-425</td><td>+202</td><td>2.6</td><td>2</td><td>4</td><td>1 ± 0.7</td></tr><tr><td>N1-453</td><td>+84</td><td>4.2</td><td>3(1)</td><td>4</td><td>0.8 ± 0.05</td></tr><tr><td>N1-458</td><td>+34</td><td>4.4</td><td>5(1)</td><td>6</td><td>0.8 ± 0.4</td></tr><tr><td>N1-454</td><td>-6</td><td>5.2</td><td>390</td><td>375</td><td>0.03 ± 0.015</td></tr><tr><td>N1-412</td><td>-26</td><td>5.2</td><td>400</td><td>385</td><td>0.022 ± 0.01</td></tr><tr><td>N1-420</td><td>-36</td><td>4.4</td><td>550</td><td>625</td><td>0.013 ± 0.008</td></tr></tbody></table>

Abbreviations: S<sub>charge</sub> = analyzed surface area of the charges; Nb cx = number of crystals observed; numbers in parentheses indicate the number of secondary skeletal crystals; Nb<sub>n</sub> cx = number of crystals, normalized to S<sub>charge</sub> = 5 mm²; L = crystal length.

*Positive and negative values superheating and underheating experiments, respectively.

This complex set of embayments includes elongated, parallel embayments 1.3 mm long and 45 µm wide and smaller elongated embayments along the internal rim of the crystal (Fig. 4), suggesting that it is similar to the two above-mentioned types of embayments, but sectioned differently.

## Subliquidus Experiments

Regardless of chemical composition, experiments initially heated to subliquidus temperatures contain far more crystals (up to one to two orders of magnitude, Table 2) than those heated to superliquidus temperatures. Crystals are always pure forsterite and the

interstitial liquid (glass after quenching) is homogeneous in each experiment (Table S1). The number of crystals increases with increasing degree of underheating (Fig. 5), but each starting composition follows a unique trend.

The mean crystal size in charges seems to be anticorrelated with the number of crystals present (Fig. 6). This relation is observed in charges performed with compositions Fo#18 and Fo#24, but not for Fo#19. The lack of correlation for Fo#19 results from the size sorting of crystals in Fo#19 charges, with smaller crystals preferentially distributed around the edges and larger ones in the center (Fig. 7a); although
<figure><img src="image_3.png" /><figcaption>Fig. 2. Optical microphotograph (a, b) of composition Fo#24, superheated to +ΔT = 10 °C before cooling, with a large olivine crystal and smaller skeletal/tabular crystals with hopper cavity (zoom in b); Gl: glass. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

such size sorting is observed for all compositions (Fig. 7b and 7c), it is more drastic for Fo#19.

In all charges from underheating experiments, olivine grain sizes are radially distributed. Each charge shows three concentric zones characterized by a different grain size. External zones near the platinum wire display numerous small olivine crystals, whereas olivines in the center are an order of magnitude larger; crystals between these two zones are of intermediate size.

In all charges, olivines are globally euhedral if isolated within the liquid (glass) or polyhedral if part of a crystal cluster. In clusters, the contact between two crystals sometimes forms a fine, long film of glass resembling an embayment (blue arrow in Fig. 8a). Crystals are not evenly distributed throughout the charges, and large areas containing fewer crystals are often present. These areas are generally located in the center of the charges, marking the above-mentioned size sorting. When a large area of liquid is present, nearby olivines usually display skeletal or dendritic overgrowths at least 20–100 µm thick (Fig. 8a). We note that one charge (Fo#18, $-\Delta T_s = 10$ °C) shows a large area of liquid, but no overgrowths on the olivines, probably due to sectioning. In contrast, the numerous crystals present in the center of charge Fo#18 ($-\Delta T_s = 42$ °C) restrict olivine overgrowth, probably due to the absence of a large volume of liquid.

Glass inclusions and embayments are rare in olivines from experiments performed under subliquidus conditions. True melt inclusions ~10 µm in diameter (Figs. 7b, 7c and 8a, 8b) and containing shrinkage bubbles are rare (e.g., Fo#18, $-\Delta T_s = 32$ °C) and mainly occur in the centers of crystals. Other melt

inclusions not containing shrinkage bubbles are present along olivine rims. These inclusions are rounded or elongate, symmetrical (Fig. 8), measure 20–50 µm long (e.g., Fo#18, $-\Delta T_s = 52$ °C; Fo#24, $-\Delta T_s = 45, 35, \text{and } 10$ °C), and are probably always connected to the silicate liquid in other planes, explaining the absence of shrinkage bubbles. These open inclusions may be related to embayments formed by dendritic overgrowths, like those observed in the superliquidus experiments.

Figure 8 highlights the different steps of melt inclusion formation, from skeletal or dendritic overgrowths producing embayments to the closure of embayments to form melt inclusions.

## Superliquidus Experiments with Various Cooling Rates for a Fixed Composition (Fo#24)

Experiments in which composition Fo#24 was superheated to a starting temperature $+\Delta T = 10$ °C and cooled at a large range of cooling rates show a slight but significant increase in crystal number (from 1–3 to 20) with increasing cooling rate from 2 to $750 \, °C \, h^{-1}$ (Table 3). Similarly, crystal shape evolves from polyhedral/skeletal to skeletal/dendritic within increasing cooling rate (Fig. 9). The transition between these morphologies occurs around $100 \, °C \, h^{-1}$ (Fig. 9e). No significant olivine chemical variations are observed in these experiments; in contrast, the liquids display chemical gradients at the olivine–liquid interface as soon as the cooling rate exceeds $5 \, °C \, h^{-1}$ (Table S2 in supporting information).

Melt inclusions and embayments are present in olivines at all cooling rates explored. Again, melt
<figure><img src="image_4.png" /><figcaption>Fig. 3. SEM images and interpretive sketches of experimental charges. a) Fo#18, superheated to +ΔT = 8 °C, and (b, c) Fo#19, superheated to +ΔT = 75 °C show large crystals of olivine with large embayments and rounded melt inclusions. Single crystals of olivine are shown in green; MI (1), type-1 melt inclusions containing shrinkage bubble; MI (2), type-2 melt inclusions without shrinkage bubble; SB, shrinkage bubble; Emb (1), type-1 embayment; Emb (2), type-2 embayment; Ogw, olivine overgrowth; Gl, glass; Ol, olivine; Pt, platinum wire. See text for descriptions of melt inclusion and embayment types. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>Fig. 4. SEM image and interpretive sketch of experimental charge Fo#24 superheated to +Δ*T* = 50 °C. Ol, olivine; Gl, glass; Emb, embayment; MI (1), type-1 melt inclusions containing shrinkage bubble; MI (2), type-2 melt inclusions without shrinkage bubble; Ogw, dendritic overgrowth of olivine. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>Fig. 5. The number of olivine crystals present in experimental charges (normalized to an analyzed surface area of 5 mm²; Table 2) as a function of Δ*T* for compositions Fo#24, Fo#18, and Fo#19. Negative/positive values of Δ*T* indicate the degree of underheating/superheating before cooling. Black line, trend line of composition Fo#18; black dotted line, trend line of composition Fo#19; gray line, trend line of composition Fo#24. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

inclusions are either true melt inclusions containing
shrinkage bubbles or glass inclusions without shrinkage
bubbles that are generally elongated and seem to be
crystallographically controlled. The shapes of
embayments vary according to cooling rate. Type-1
embayments (i.e., long, winding, and narrow; Fig. 9a)
are observed in experiments that cooled relatively slowly
(≤10 °C h⁻¹). At faster cooling rates, embayments are
more numerous and angular, that is, limited by olivine
facets, similar to type-2 embayments that formed by
dendritic overgrowths in superliquidus and subliquidus

experiments. However, in this case, embayments occur
in internal cavities of hopper crystals that correspond to
the initial growth morphology (Donaldson, 1976; Faure,
Trolliard, Nicollet, et al., 2003), not a subsequent
overgrowth step.

DISCUSSION

The solidification of magmas in general, and
chondrules in particular, depends primarily on
crystal nucleation and secondly on crystallization
<figure><img src="image_7.png" /><figcaption>Fig. 6. Numbers and sizes of olivine crystals in experimental charges (normalized to an analyzed surface area of 5 mm²; Table 2) as a function of Δ*T* for the different compositions studied (Fo#24, Fo#23, Fo#18, and Fo#19). Negative/positive values of Δ*T* indicate the degree of underheating/superheating before cooling. Red dashed lines, liquidus temperatures for each composition; blue shaded area, no crystals formed. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

(Lofgren, 1983; Lofgren & Russell, 1986). Therefore, deciphering crystal textures to trace their thermal history requires consideration of the effects of both processes.

## Nucleation Controls Final Texture

### Effect of Initial Temperature

The initial temperatures of experiments, relative to the liquidus, seem to be the major parameter controlling the number of crystals present after cooling. Indeed, the number of crystals varies by one to two orders of magnitude between superliquidus and subliquidus experiments; for all composition considered, superliquidus experiments show up to two to six crystals per charge, whereas subliquidus experiments crystallize hundreds of crystals, except for one experiment with composition Fo#24 with a small degree of underheating (−Δ*T*<sub>s</sub> = 10 °C), which shows only 39 crystals

(normalized to an analyzed surface area of 5 mm²; Table 2). This result is also consistent with previous studies performed using other starting compositions (Hewins, 1983, 1989; Lofgren, 1989). Therefore, the composition of the starting liquid does not seem to be a critical parameter. In contrast, the number of crystals formed can be, in a first-order approximation, linked to the nucleation rate of the cooling silicate liquid if no mechanism such as Ostwald ripening occurs during crystallization. Although Ostwald ripening experiments have shown that the number of olivine crystals can decrease by more than two orders of magnitude over 496 h (Cabane et al., 2005), it is unlikely that this mechanism occurred in our experiments (longer than 200 h) because the driving force of Ostwald ripening is the minimization of the total interfacial energy, which is weak compared to the chemical driving force, that is, liquid supersaturation due to cooling, in our experiments. Therefore, the degree of superheating is
<figure><img src="image_8.png" /><figcaption>Fig. 7. SEM images of subliquidus experimental charges displaying (a) strong crystal size zonation (Fo#19, -Δ*T*<sub>s</sub> = 20 °C) and (b) the presence of melt inclusions within larger olivine crystals (Fo#18, -Δ*T*<sub>s</sub> = 32 °C). c) Enlarged view of the red square in (b) showing two true melt inclusions containing shrinkage bubbles. Ol, olivine; Gl, glass; MI, melt inclusion; SB: shrinkage bubble. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>Fig. 8. SEM images of subliquidus experimental charges showing: (a) the formation of pseudo-embayments along the contact between two olivine crystals, marked by the blue arrow (Fo#24, -Δ*T*<sub>s</sub> = 10 °C); and (b) how the evolution of dendritic overgrowths forms melt inclusions (Fo#24, -Δ*T*<sub>s</sub> = 35 °C). Ol, olivine (in green); MI, melt inclusion; Ogw, olivine overgrowth; Emb (2), type-2 embayment; Pt, platinum wire. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

the most important factor limiting the nucleation sites
in the silicate liquid.

Moreover, when the degree of superheating is
sufficiently high (+Δ*T* > 226 °C, Fo#23; Table 2), the

nucleation is completely suppressed, consistent with the
results of Donaldson (1979) that showed that nucleation
is increasingly delayed with increasing degree of
superheating. Although their results did not show the
<table><caption>Table 3. Numbers and shapes of olivine crystals formed during experiments initially superheated to +ΔT = 10 °C then cooled at various rates.</caption><thead><tr><th>Run no.</th><th>Cooling rate (°C h<sup>-1</sup>)</th><th>S<sub>charge</sub> (mm<sup>2</sup>)</th><th>Nb cx</th><th>Nb<sub>n</sub> cx</th><th>Shape</th></tr></thead><tbody><tr><td>N1-424</td><td>750</td><td>5.3</td><td>16</td><td>15</td><td>skel/dend</td></tr><tr><td>N1-413</td><td>100</td><td>3.3</td><td>13</td><td>20</td><td>skel/dend</td></tr><tr><td>N1-415</td><td>50</td><td>7.4</td><td>11</td><td>10</td><td>skel</td></tr><tr><td>N1-414</td><td>10</td><td>7.4</td><td>4</td><td>3</td><td>skel</td></tr><tr><td>N1-423</td><td>5</td><td>3.4</td><td>2(1)</td><td>3</td><td>skel</td></tr><tr><td>N1-382</td><td>2</td><td>3.5</td><td>3(2)</td><td>1</td><td>polyh</td></tr></tbody></table>

Abbreviations: S<sub>charge</sub> = analyzed surface area of the charges; Nb cx = number of crystals observed; numbers in parentheses indicate the number of secondary skeletal crystals; Nb<sub>n</sub> cx = number of crystals, normalized to S<sub>charge</sub> = 5 mm<sup>2</sup>; skel = skeletal; dend = dendritic; polyh = polyhedral.

total suppression of olivine nucleation because they investigated lower degrees of superheating (+ΔT < 125 °C), extrapolation of their results suggests that for sufficiently high degrees of superheating, nucleation would occur below the glass transition temperature, which seems unlikely. Moreover, experiments performed to determine the maximum temperature of chondrule formation imply that the degree of superheating could not have exceeded +400 °C; otherwise, chondrules would have remained liquid (i.e., vitreous after quenching) and particular textures such as BOs (i.e., dendritic olivines) could not have crystallized at any cooling rate used (Connolly et al., 1998). The variable degrees of superheating required to suppress nucleation in these previous studies can be explained by their different starting liquid compositions and/or experimental protocols. In particular, a recent study demonstrated that the magnitude of superheating must integrate both the degree of superheating and the time spent above the liquidus (First et al., 2020). In any case, the critical degree of superheating required to suppress nucleation can be refined for a given composition.

## Effect of Cooling Rate

Another parameter affecting the final number of crystals present is the cooling rate in superliquidus experiments. Although the cooling rate in superliquidus experiments has a less important effect on the final number of crystals (varying by a factor of 3–5) than the initial temperature relative to the liquidus (crystal number varying by several orders of magnitude), the effect of the cooling rate is significant. Indeed, at slow cooling rates (<10 °C h<sup>-1</sup>), only three to four crystals are consistently present in the charges, but at faster cooling rates, the number of crystals increases by a factor of 3–5 (Table 3). A similar result was observed

by Walker et al. (1976) during the experimental crystallization of lunar picritic basalt at various cooling rates. This result is important because the impact of cooling rate on nucleation is generally considered in terms of increased nucleation undercooling (Donaldson, 1979; Tsuchiyama, 1983) and discussed with time-temperature-transformation diagrams to constrain the formation of crystal-free glass (Vetere et al., 2013, 2015). However, whatever the aims of these studies, all results seem consistent with transient nucleation theory, which predicts that the incubation time of crystal nuclei should decrease with decreasing temperature (i.e., increasing cooling rate; Kaschiev, 1969).

This concept is schematized in Fig. 10 to highlight the principal parameters impacting nucleation; the impact of cooling rate on nucleation is considered in relation to the curve that delimits crystal-free (i.e., no nucleation) from crystal-bearing glasses (i.e., nucleation always occurs).

This boundary delimits the instant that clusters of atoms or molecules in the liquid are stable enough, that is, sufficiently large, to grow to macroscopic dimensions. At that instant, the radii of nuclei are equal to or larger than the critical radius *r*\* and crystal growth can begin. The critical radius depends on various parameters including initial temperature (i.e., superliquidus versus subliquidus experiments), time, cooling rate, and composition (Donaldson, 1979). At slow cooling rates, the nucleation event occurs at higher temperatures or lower degrees of undercooling; *r*\* is large; and the probability that nuclei will grow to reach *r*\* is very low. Therefore, few nuclei, and thus few crystals, grow. In contrast, at fast cooling rates, nucleation occurs at lower temperatures (higher degrees of undercooling) and *r*\* is small, facilitating nucleation and producing numerous crystals. Because *r*\* decreases with increasing degree of undercooling, clusters require less time to achieve the critical radius at higher than at lower degrees of undercooling, and the delay in nucleation (incubation period) is reduced at high degrees of undercooling (Fig. 10a).

Our results are consistent with this relation and the results of Walker et al. (1976) that link increased cooling rates to higher numbers of crystals (Fig. 11). Because the degrees of undercooling required for nucleation to occur increases with increasing cooling rate (Donaldson, 1979), we can compare the nucleation density (defined here as the number of crystals per mm<sup>2</sup>) to the degree of undercooling via the cooling rate (Fig. 10b). Although nucleation density is not necessarily equivalent to nucleation rate in our experiments because the charges were cooled at various rates and quenched at the same temperature, a
<figure><img src="image_10.png" /><figcaption>Fig. 9. a–f) SEM and (g, h) transmitted petrographic microphotographs showing the evolution of olivine crystal shapes with increased cooling rate (Fo#24, +ΔT = 10 °C). Cooling rates: (a) 2 °C h⁻¹, (b) 5 °C h⁻¹, (c) 10 °C h⁻¹, (d) 50 °C h⁻¹, (e) 100 °C h⁻¹, (f) 750 °C h⁻¹, and (g, h) 100 °C h⁻¹. In (g, h), olivine dendrites are clearly observed within the residual glass. MI (2), type-2 melt inclusion without shrinkage bubble; Emb (1), type-1 embayment; Ogw, dendritic olivine overgrowth; Dend, dendrite. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>
<figure><img src="image_11.png" /><figcaption>Fig. 10. Schematic diagrams of nucleation in initially superheated melts. a) Time-temperature-transformation diagram with different cooling rates and associated degrees of undercooling at nucleation (−Δ*T*<sub>X</sub>; modified after Kaschiev [1969] and Donaldson [1979]). Sketches show different textures (shapes and numbers of crystals) obtained at different cooling rates. The critical radius for nuclei (*r*\*) increases upward. The black solid curve delimits the field where nucleation is suppressed at high temperature from that where nucleation occurs. *T*<sub>liq</sub>, liquidus temperature; +Δ*T*, initial degree of superheating; *T*<sub>quench</sub>, quench temperature. b) Nucleation density of olivine crystals (number of crystals/mm²) versus cooling rate (CR). (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

qualitatively similar relationship is observed for both nucleation density and nucleation rate. This shape similarity is consistent with the fact that nucleation occurs at small degrees of undercooling for slow cooling rates because the incubation time is long, whereas faster cooling rates (i.e., shorter incubation times) increase the degree of undercooling at nucleation. Therefore, nucleation density can be used to estimate cooling rate.

## Nucleation Growth Competition Reduces Liquid Supersaturation

It is well known that crystal shape evolves as a function of the degree of supersaturation of the liquid from which they are forming (Sunagawa, 1981). An

alternative is to consider the degree of undercooling (−Δ*T*) rather than the degree of supersaturation (−Δ*C*) as the two parameters are linked (Faure & Tissandier, 2014). Therefore, whatever the parameter used, numerous studies have shown that crystal shape evolves from euhedral or polyhedral at small degrees of undercooling to skeletal and dendritic at greater degrees of undercooling or supersaturation (Donaldson, 1976; Faure, Trolliard, Nicollet, et al., 2003). One way to increase the degree of undercooling is to impose a fast cooling rate. Therefore, cooling rate does not directly control the evolution of crystal morphology, but serves, among other parameters including thermal or compositional gradients (Bouquain et al., 2014; Faure et al., 2006; Laumonier et al., 2019), to increase the
<figure><img src="image_12.png" /><figcaption>Fig. 11. Nucleation density of olivine crystals versus cooling rates; data from this study and Walker et al. (1976). CR, cooling rate.</figcaption></figure>

degree of undercooling (Lofgren & Lanier, 1990). Thus, slow cooling rates induce low degrees of undercooling, producing euhedral or polyhedral crystal morphologies. In contrast, faster cooling rates allow the development of skeletal shapes at moderate degrees of undercooling and dendritic morphologies at higher degrees of undercooling (Faure, Trolliard, Nicollet, et al., 2003).

This general trend is globally consistent with our cooling experiments at various cooling rates (Table 3; Fig. 9). Indeed, rapid cooling experiments produce skeletal and dendritic olivines whereas slow cooling rates produce olivines whose shapes are limited by well faceted external (i.e., polyhedral morphology). However, the internal parts of these polyhedral crystals show elongated glass zones that correspond to glass inclusions stricto sensu if they are totally isolated from the external melt or embayments if they remain connected with the mesostasis. Such elongated glass zones within polyhedral crystals have been produced in previous experiments with two cooling stages: a first slow cooling stage to crystallize euhedral crystals followed by a rapid cooling stage to produce skeletal overgrowths (Faure et al., 2007). However, in our and previous experiments (Faure et al., 2012, 2017), elongated glass inclusions lato sensu (i.e., open or closed inclusions) are present within crystals formed during a single slow cooling stage. This apparent contradiction is easily explained by the fact that nucleation is suppressed at low degrees of undercooling because the critical radius is large, resulting in an extensive incubation time (see previous section). Then, when nuclei attain critical size, the few viable nuclei exist within a supersaturated liquid because nucleation was delayed. Therefore, these nuclei grow rapidly, developing either skeletal or dendritic

morphologies as a function of the degree of undercooling or supersaturation. This nucleation growth history is similar to the crystallization history obtained for isothermal experiments (Donaldson, 1976; Mourey & Shea, 2019; Shea et al., 2019) in which charges were cooled very rapidly from superliquidus temperatures to a fixed subliquidus temperature and held isothermally before quenching. As a function of the time they were held isothermally, crystals evolve from skeletal or dendritic at the beginning of growth to polyhedral after longer durations.

Therefore, crystal texture depends not only on the nucleation step but also the growth process, which develops various crystal morphologies as a function of the degree of supersaturation. However, crystallization histories are not always limited to an initial nucleation step following by growth (fast or slow) to return to equilibrium conditions.

Indeed, charges cooled slowly after a period of superheating can display both large polyhedral and small skeletal crystals (Fig. 2). This observation implies that nucleation is not limited to a single event, but can occur several times during cooling. The large difference in size between the two generations of olivine crystals indicates that nucleation is not continuous, but corresponds to two distinct events. This resumption of nucleation is interpreted as the result of local liquid supersaturation due to the incapacity of large polyhedral crystals to grow fast enough to suppress supersaturation far away, that is, throughout the entire charge (Faure & Tissandier, 2014). This observation demonstrates that efficient nucleation requires supersaturation of the liquid. However, the degree of supersaturation during the second nucleation event is relatively low because the few newly formed crystals
<figure><img src="image_13.png" /><figcaption>Fig. 12. Steps of embayment formation during the slow cooling of a liquid after superheating. MI, melt inclusion; Emb (1), type-1 embayment; Emb (2), type-2 embayment associated with overgrowth (Ogw). (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

initially display tabular forms. Then, the evolution of these new crystals from tabular to hopper (skeletal) morphologies implies an increase in the degree of supersaturation. Importantly, this increase in the degree of supersaturation must have occurred throughout the entire charge because large, polyhedral crystals also display skeletal overgrowths. Therefore, even at slow cooling rates (2 °C h⁻¹), polyhedral crystals can evolve toward skeletal or dendritic shapes without an increase in the cooling rate.

This result is consistent with the decreasing diffusion rates of species within the silicate liquid as temperature decreases. Crystal growth becomes controlled by diffusion and the resulting crystal morphology is either skeletal or dendritic depending on the size of the boundary layer that develops at the crystal-liquid interface (Faure & Schiano, 2005). Therefore, the distance between crystals, or the sphere of influence of each crystal in the liquid, plays a major role in decreasing the degree of supersaturation throughout the charge. This effect is well illustrated by subliquidus experiments, in which numerous small crystals formed (Fig. 8). These small crystals always show polyhedral shapes except in areas with large pools of liquid. These zones generally occur in the center of the charge and correspond to a well-known

experimental artifact due to crystal settling in long duration experiments with low viscosity liquids due to settling of crystals (Donaldson, 1977; Faure et al., 2017; Lofgren, 1989; Zieg & Lofgren, 2006). Crystals that grow toward these pools of liquid show skeletal or dendritic overgrowths whereas all other crystals in the same charge show polyhedral shapes (Fig. 7). This demonstrates that, for similar thermal conditions, liquid supersaturation can be completely erased without rapid crystal growth if enough crystals are present and their spheres of influence overlap. In contrast, if few crystals are present and/or broadly distributed throughout the charge, liquid supersaturation increases in crystal-free zones. Any crystals located near these supersaturated areas develop rapid growth morphologies to decrease the local degree of supersaturation. In this case, then, the resulting texture depends not only on nucleation and growth but also on the crystals' spatial distribution.

## Formation of Melt Inclusions

By considering nucleation events and growth processes during the crystallization history of the experimental charges, we here show that the formation of melt inclusions can occur at various times (Fig. 12).
<figure><img src="image_14.png" /></figure>

<figure><img src="image_15.png" /><figcaption>Fig. 13. Schematic diagrams summarizing the textural evolution of olivine as a function of time and temperature for slow cooling rates in (a) superliquidus and (b) subliquidus experiments. Orange areas correspond to locally supersaturated zones. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>
The first episode of melt inclusion formation is linked to the initial nucleation event (Fig. 13a). In the case of delayed nucleation, the few viable nuclei will grow rapidly, reducing the degree of liquid supersaturation. These crystals initially grow in skeletal or dendritic shapes, but then evolve toward polyhedral morphologies as the degree of supersaturation decreases (Fig. 12). Long and generally sinuous embayments (type 1) result from this crystal-shaped evolution. Because these embayments are macroscopic defects within the crystal, having a high surface energy compared to their volume energy, they tend to segment into small pools of liquid to decrease the interfacial energy. This process eventually produces true melt inclusions, that is, containing shrinkage bubbles that demonstrate they are separated from the external liquid. This hypothesis is consistent with our observation that in rapidly cooled charges, melt inclusions are observed within the skeletal core of dendritic crystals in addition to two large open cavities, that is, embayments as classically described (Donaldson, 1976; Faure, Trolliard, Nicollet, et al., 2003). Such rapid closure of thin embayments to produce true melt inclusions is in agreement with the observation that textural ripening, that is, decreasing the interfacial energy, is concomitant with dendritic growth (Faure, Trolliard, & Soulestin, 2003).

The second episode of melt inclusion formation is due to an increase in the degree of supersaturation during crystallization because polyhedral crystals, probably controlled by interfacial processes, cannot grow fast enough to decrease the degree of liquid supersaturation. As mentioned in the previous section, this increase in the degree of liquid supersaturation is mostly linked to the spatial distribution of crystals within the charge, that is, to crystals' spheres of influence, in both superliquidus and subliquidus experiments (Fig. 13a and 13b). If crystals' spheres of influence do not overlap, areas of supersaturated liquid can develop far from the crystals. Consequently, crystals grow rapidly with skeletal or dendritic morphologies, acting against this local supersaturation (Fig. 12). Such textural ripening by skeletal or dendritic overgrowth will eventually close embayments, producing a new generation of melt inclusions.

Except, perhaps, for rare, true melt inclusions observed in small olivine crystals formed in subliquidus experiments (Figs. 7b and 8b) that could correspond to the impingement of screw dislocations during slow growth (Faure & Schiano, 2005), all other inclusions seem to result from an initial step of rapid growth followed by a period of slow growth. A similar scenario was proposed to explain phosphorous zonations in natural olivines (Manzini et al., 2017; Welsch et al., 2014).

It should be possible to determine nucleation temperature, that is, the degree of undercooling, from

<figure><img src="image_16.png" /><figcaption>Fig. 14. Cooling rates used to produce various chondrule textures (porphyritic, macro-porphyritic, and barred texture) with dwell time <2 h (except [1], with a dwell time of 17 h). Numbers denote different experimental investigations: (1) Lofgren and Russell (1986); (2) Lofgren (1989); (3) Jones and Lofgren (1993); (4) Radomsky and Hewins (1990); (5) Wick and Jones (2012); (6) Lofgren and Lanier (1990); (7) Kennedy et al. (1993); (8) Tsuchiyama et al. (2004); (9) this study. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

glass inclusions lato sensu because their shape and location within the crystal depend on the degree of undercooling (Mourey & Shea, 2019), via the entrapping crystal's morphology (Colin et al., 2012; Faure & Schiano, 2005; Welsch et al., 2009). Although the specific arrangement of inclusions is eventually erased by further crystal growth in polyhedral crystals, chemical zonations (e.g., P, Al, Ni) should reflect the initial crystal growth morphology (Borisova et al., 2014; Bouvet de Maisonneuve et al., 2016; Libourel & Portail, 2018; Milman-Barris et al., 2008; Salas et al., 2021; Shea et al., 2019; Welsch et al., 2013, 2014).

## Implications for Chondrule Crystallization

Numerous experimental studies have evidenced the role of cooling rate (Fig. 14) and heterogeneous nucleation in producing porphyritic textures (Lofgren, 1989; Lofgren & Russell, 1986; Radomsky & Hewins, 1990; Tsuchiyama & Nagahara, 1981). Unlike homogeneous nucleation, heterogeneous nucleation occurs on substrates, such as impurities present in the liquid (dust or grains). The substrate locally decreases the activation energy and therefore reduces the incubation time for nucleation. Therefore, if only partial
<figure><img src="image_17.png" /><figcaption>Fig. 15. Photomicrographs (cross-polarized light) of chondrules demonstrating the inverse relation between crystal size and abundance. a) Porphyritic olivine chondrule displaying numerous polyhedral olivine crystals (Allende CV 3); (b) macro-porphyritic olivine chondrule showing only four large olivines with numerous embayments (Felix CO 3). (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

melting affected chondrule precursors, numerous crystals would have formed from relict crystals or nuclei already present at the beginning of cooling. With increasing degree of melting, depending on peak temperature, the duration of heating, and the size of precursors, the resulting texture will be cryptoporphyritic, micro-porphyritic, or porphyritic. In contrast, the BO texture results from complete melting (Connolly et al., 1998; Lofgren, 1989; Tsuchiyama et al., 2004) and thus delimits partial from total melting.

This limit is marked by a drastic change in the number of olivine crystals present within a chondrule, indicating the crucial role of nucleation. Although our experiments did not reproduce the BO texture, we observed a significant change in the final number of crystals when charges were heated to or above the liquidus, which precisely fixed the conditions of total melting (Fig. 6). Indeed, kinetic issues related to melting were not considered in our experiments, which produced the macro-PO texture as defined by Jones (1992) instead of the BO texture. The macro-PO texture is generally not considered in the gradual textural evolution framework established above as a function of increasing degree of melting. Therefore, we propose to include the macro-PO texture with the BO texture in the textural framework because both mark the total melting of chondrules:

$$ \text{crypto-porphyritic} \rightarrow \text{micro-porphyritic} \rightarrow \text{porphyritic olivine} \rightarrow \text{BO} + \text{macro porphyritic olivine} $$

In a tentative attempt to classify textures unambiguously, Hewins and Fox (2004) suggested using olivine nominal grain size based on number density.

BOs are larger than 100 {m, whereas intermediate PO texture varies from porphyritic (40–100 {m} to micro-porphyritic (10–40 {m} to crypto-porphyritic (<10 {m}). In this scheme, macro-PO texture ranges in size from 100 to 600 {m (Jones, 1992) and can again be associated with the BO. The number of olivine crystals present is also an important parameter and is directly related to crystal size; in the finite volume of a chondrule, crystals cannot be numerous if they are large (Fig. 15). Therefore, to distinguish olivine size between textural types (Hewins & Fox, 2004), we suggest that using the number of crystals per surface area and crystal shape would be less ambiguous (Zieg & Lofgren, 2006).

The fact that the macro-PO texture implies complete melting has two important implications. First, porphyritic textures in chondrules are not necessarily synonymous with partial melting as generally considered; the detailed texture, including the size and shape of olivines as well as their abundance per unit area (or volume, when known), should be considered when evaluating the extent of melting. Second, isolated olivine grains are sometimes related to macro-PO chondrules. Although it remains disputed whether this filiation results from condensation from the nebular (Fuchs et al., 1973; Olsen & Grossman, 1978; Steele, 1986; Weinbruch et al., 2000) or the destruction of macro-porphyritic chondrules (Jones, 1992; Jones et al., 2000; Richardson & McSween, 1978; Roedder, 1981), the recent study of Jacquet et al. (2021) favored the latter. Within isolated olivine grains, the presence of glass inclusions and long embayments (Steele, 1986; Weinbruch et al., 2000) similar to our type-1 embayments is consistent with a common origin for isolated olivines and olivine
in macro-porphyritic chondrules. Moreover, type-1 embayments were only obtained from superliquidus experiments, consistent with the fact that macro-porphyritic texture chondrules initially suffered complete melting.

## CONCLUSIONS

Our experimental results confirm that nucleation exerts a strong control on the various textures observed in chondrules. In particular, the number of crystals present differs by one to two orders of magnitude between experiments that were initially heated above or below their liquidus temperature. However, the extent of melting also controls the final chondrule texture. Indeed, the degree of melting depends on both the peak temperature and the duration of heating. Nevertheless, two groups of chondrules can be broadly distinguished as a function of the extent of initial melting; the first corresponds to partial initial melting and encompasses GO, crypto-porphyritic, micro-porphyritic, and porphyritic chondrules, whereas the second corresponds to complete initial melting and encompasses BO and/or pyroxene, RP, and CC. Moreover, our experimental results show that macro-PO textures are associated with the latter group, that is, complete initial melting.

Furthermore, the morphology, large size, and small number of olivines observed in macro-porphyritic chondrules, as well as the embayments and melt inclusions they host, suggest that olivines result from an initial period of rapid growth due to delayed nucleation during slow cooling within the chondrule. Indeed, if macro-porphyritic chondrules had cooled faster, they would contain smaller, more numerous crystals with skeletal or dendritic morphologies, as in Ca-Al-rich chondrules (Nagahara et al., 2009; Rubin, 2004).

Our experimental results also show that melt inclusions form after episodes of rapid crystal growth, which can occur several times, even if the cooling rate of the system is relatively slow.

**Acknowledgments**—We thank Robert Dennen (RD Editing Services) for improving the English language of the paper. Roger Hewins and Dominik Hezel provided fruitful reviews that improved the manuscript. The manuscript was also greatly improved by the comments of Editor Kevin Righter, who is also thanked for the editorial handling of this paper. This research was financed by the Région Grand Est in France. This study was supported by the Programme National de Planétologie: PNP-INSU. Many thanks to Yves Marrocchi, the CRPG, and the Museum National d'Histoire Naturelle de Paris for lending the two thin

sections of the chondrites Allende and Félix. This is CRPG contribution number 2822.

*Data Availability Statement*—The data that support the findings of this study are available in the supplementary material of this article.

**Editorial Handling**—Dr. Kevin Righter

## REFERENCES

Barosch, J., Hezel, D. C., Ebel, D. S., and Friend, P. 2019. Mineralogically Zoned Chondrules in Ordinary Chondrites As Evidence for Open System Chondrule Behavior. *Geochimica et Cosmochimica Acta* 2494: 1–16.

Barosch, J., Hezel, D. C., Sawatzki, L., Halbauer, L., and Marrocchi, Y. 2020. Sectioning Effects of Porphyritic Chondrules: Revising the PP/POP/PO Classification and Correcting Modal Abundances of Mineralogically Zoned Chondrules. *Meteoritics & Planetary Science* 55: 993–9.

Borisova, A. Y., Faure, F., Deloule, E., Grégoire, M., Béjina, F., de, Parseval, P., and Devidal, J.-L. 2014. Lead Isotope Signatures of Kerguelen Plume-Derived Olivine-Hosted Melt Inclusions: Constraints on the Ocean Island Basalt Petrogenesis. *Lithos* 198-199: 153–71.

Bouquain, S., Arndt, N. T., Faure, F., and Libourel, G. 2014. An Experimental Study of Pyroxene Crystallization During Rapid Cooling in a Thermal Gradient: Applications to Komatiites. *Solid Earth* 5: 641–50.

Bouvet de Maisonneuve, C., Costa, F., Huber, C., Vonlanthen, P., Bachmann, O., and Dungan, M. A. 2016. How Do Olivines Record Magmatic Events? Insights from Major and Trace Element Zoning. *Contributions to Mineralogy and Petrology* 171: 56.

Burkhardt, C., Kleine, T., Dauphas, N., and Weiler, R. 2012. Nucleosynthetic Tungsten Isotope Anomalies in Acid Leachates of the Murchison Chondrite: Implications for Hafnium-Tungsten Chronometry. *The Astrophysical Journal Letters* 753: 6.

Cabane, H., Laporte, D., and Provost, A. 2005. An Experimental Study of Ostwald Ripening of Olivine and Plagioclase in Silicate Melts: Implications for the Growth and Size of Crystals in Magmas. *Contributions to Mineralogy and Petrology* 150: 37–53.

Colin, A., Faure, F., and Burnard, P. 2012. Timescales of Convection in Magma Chambers Below the Mid-Atlantic Ridge from Melt Inclusions Investigation. *Contributions to Mineralogy and Petrology* 164: 677–91.

Connelly, J. N., Bizzarro, M., Krot, A. N., Nordlunds, A., Wielandt, D., and Ivanova, M. A. 2012. The Absolute Chronology and Thermal Processing of Solids in the Solar Protoplanetary Disk. *Science* 338: 651–5.

Connolly, H. C. Jr., and Hewins, R. H. 1995. Chondrules As Products of Dust Collisions with Totally Molten Droplets within a Dust-Rich Nebular Environment: An Experimental Investigation. *Geochimica et Cosmochimica Acta* 59: 3231–46.

Connolly, H. C. Jr., Jones, B. D., and Hewins, R. H. 1998. The Flash Melting of Chondrules: An Experimental Investigation into the Melting History and Physical Nature
of Chondrule Precursors. *Geochimica et Cosmochimica Acta* 62: 2725-35.

Donaldson, C. H. 1976. An Experimental Investigation of Olivine Morphology. *Contributions to Mineralogy and Petrology* 57: 187-213.

Donaldson, C. H. 1977. Laboratory Duplication of Comb Layering in the Rhum Pluton. *Mineralogical Magazine* 41: 323-36.

Donaldson, C. H. 1979. An Experimental Investigation of the Delay in Nucleation of Olivine in Mafic Magmas. *Contributions to Mineralogy and Petrology* 69: 21-32.

Faure F. 2020. Early Silica Crust Formation in Planetesimals by Metastable Silica-Rich Liquid Immiscibility or Cristobalite Crystallisation: The Possible Origin of Silica-Rich Chondrules. *Scientific Reports* 10: 4765. https://doi.org/10.1038/s41598-020-61806-5

Faure, F., Arndt, N., and Libourel, G. 2006. Formation of Spinifex Texture in Komatiites: An Experimental Study. *Journal of Petrology* 47: 1591-610.

Faure, F., and Schiano, P. 2005. Experimental Investigation of Equilibration Conditions During Forsterite Growth and Melt Inclusion Formation. *Earth and Planetary Science Letters* 236: 882-98.

Faure, F., Schiano, P., Trolliard, G., Nicollet, C., and Soulestin, B. 2007. Textural Evolution of Polyhedral Olivine Experiencing Rapid Cooling Rate. *Contributions to Mineralogy and Petrology* 153: 405-16.

Faure, F., and Tissandier, L. 2014. Contrasted Liquid Lines of Descent Revealed by Olivine-Hosted Melt Inclusions and the External Magma. *Journal of Petrology* 55: 1779-98.

Faure, F., Tissandier, L., Florentin, L., and Devineau, K. 2017. A Magmatic Origin for Silica-Rich Glass Inclusions Hosted in Porphyritic Magnesian Olivines in Chondrules: An Experimental Study. *Geochimica et Cosmochimica Acta* 204: 19-31.

Faure, F., Tissandier, L., Libourel, G., Mathieu, R., and Welsch, B. 2012. Origin of Glass Inclusions Hosted in Magnesian Porphyritic Olivines Chondrules: Deciphering Planetesimal Compositions. *Earth and Planetary Science Letters* 319-320: 1-8.

Faure, F., Trolliard, G., Nicollet, C., and Montel, J. M. 2003. A Developmental Model of Olivine Morphology as a Function of the Cooling Rate and the Degree of Undercooling. *Contributions to Mineralogy and Petrology* 145: 251-63.

Faure, F., Trolliard, G., and Soulestin, B. 2003. TEM Investigation of Forsterite Dendrites. *American Mineralogist* 88: 1241-50.

First, E. C., Leonhardi, T. C., and Hammer, J. E. 2020. Effects of Superheating Magnitude on Olivine Growth. *Contributions to Mineralogy and Petrology* 175: 13.

Fuchs, L. H., Olsen, E., and Jensen, K. J. 1973. Mineralogy, Mineral Chemistry and Composition of the Murchison (C2) Meteorite. *Smithsonian Contributions to the Earth Sciences* 10: 1-39.

Gooding, J. L., and Keil, K. 1981. Relative Abundances of Chondrules Primary Textural Type in Ordinary Chondrites and Their Bearing on Conditions of Chondrule Formation. *Meteoritics & Planetary Science* 16: 17-43.

Grossman, J. N., Rubin, A. E., Nagahara, N., and King, E. A. 1988. Properties of Chondrules. In *Meteorites and the Early Solar System*, edited by J. F. Kerridge and M. S. Matthews, 680-96. Tucson, Arizona: University of Arizona Press.

Hewins R. H. 1983. Dynamic Crystallization Experiments As Constraints on Chondrule Genesis. In *Chondrules and Their Origins*, edited by King E. A. Houston, Texas: Lunar and Planetary Institute, pp. 122-33.

Hewins, R. H. 1989. The Evolution of Chondrules. *Proceedings of the NIPR Symposium on Antarctic Meteorites* 2: 202-22.

Hewins, R. H. 1991. Retention of Sodium During Chondrule Melting. *Geochimica et Cosmochimica Acta* 55: 935-42.

Hewins, R. H., and Fox, G. E. 2004. Chondrule Textures and Precursor Grain Size: An Experimental Study. *Geochimica et Cosmochimica Acta* 68: 917-26.

Ivanova, A. M. 2016. Ca-Al-Rich Inclusions in Carbonaceous Chondrites: The Oldest System Objects. *Geochemistry International* 54: 387-402.

Jacquet, E., Alard, O., and Gounelle, M. 2012. Chondrule Trace Element Geochemistry at the Mineral Scale. *Meteoritics & Planetary Science* 47: 1695-714.

Jacquet, E., Piralla, M., Kersaho, P., and Marrocchi, Y. 2021. Origin of Isolated Olivine Grains in Carbonaceous Chondrites. *Meteoritics & Planetary Science* 56: 13-33.

Jones, H. R. 1992. On the Relationship Between Isolated and Chondrule Olivine Grains in the Carbonaceous Chondrite ALHA77307. *Geochimica et Cosmochimica Acta* 56: 467-82.

Jones, H. R. 1994. Petrology of FeO-Poor, Porphyritic Pyroxene Chondrules in the Semarkona Chondrite. *Geochimica et Cosmochimica Acta* 58: 5325-40.

Jones, R., Libourel, G., and Villeneuve, J. 2018. Thermal Histories of Chondrules: Petrologic Observations and Experimental Constraints. In *Chondrules and the Protoplanetary Disk*, edited by S. Russell, A. Krot, and H. Connolly, 57-90. Cambridge University Press.

Jones, H. R., and Lofgren, G. E. 1993. A Comparison of Fe-Rich, Porphyritic Olivine Chondrules in Unequilibrated Chondrites and Experimental Analogues. *Meteoritics & Planetary Science* 28: 213-21.

Jones, R. H., Saxton, J. M., Lyon, I. C., and Turner, G. 2000. Oxygen Isotopes in Chondrule Olivine and Isolated Olivine Grains from the CO3 Chondrite Allan Hills A77307. *Meteoritics & Planetary Science* 35: 849-57.

Kaschiev, D. 1969. Solution of the Non-Steady State Problem in Nucleation Kinetics. *Surface Science* 14: 209-20.

Kennedy, A. K., Lofgren, G. E., and Wasserburg, G. J. 1993. An Experimental Study of Trace Element Partitioning Between Olivine, Orthopyroxene and Melt in Chondrules: Equilibrium Values and Kinetic Effects. *Earth and Planetary Science Letters* 115: 177-95.

Laumonier, M., Laporte, D., Faure, F., Provost, A., Schiano, P., and Ito, K. 2019. An Experimental Study of Dissolution and Precipitation of Forsterite in a Thermal Gradient: Implications for Cellular Growth of Olivine Phenocrysts in Basalt and Melt Inclusion Formation. *Contributions to Mineralogy and Petrology* 174: 94.

Lauretta, D. S., Nagahara, H., and Alexander, C. M. O'D. 2006. Petrology and Origin of Ferromagnesian Silicates Chondrules. In *Meteorites and Early Solar System*, edited by D. S. Lauretta, and H. Y. McSween Jr., 2nd ed. 431-59. Tucson, Arizona: The University of Arizona.

Libourel, G., Krot, A. N., and Tissandier, L. 2006. Role of Gas-Melt Interaction During Chondrule Formation. *Earth and Planetary Science Letters* 251: 232-40. https://doi.org/10.1016/j.epsl.2006.09.011.
Libourel, G., and Portail, M. 2018. Chondrules as Direct Thermochemical Sensors of Solar Protoplanetary Disk Gas. *Science Advances* 4: 3321.

Lofgren, G. E. 1983. Effect of Heterogeneous Nucleation on Basaltic Textures: A Dynamic Crystallization Study. *Journal of Petrology* 24: 229-55.

Lofgren, G. E. 1989. Dynamic Crystallization of Chondrule Melts of Porphyritic Olivine Composition: Textures Experimental and Natural. *Geochimica et Cosmochimica Acta* 53: 461-70.

Lofgren, G. E., and Lanier, A. B. 1990. Dynamic Crystallization Study of Barred Olivine Chondrules. *Geochimica et Cosmochimica Acta* 54: 3537-51.

Lofgren, G. E., and Russell, W. J. 1986. Dynamic Crystallization of Chondrule Melts of Porphyritic and Radial Pyroxene Composition. *Geochimica et Cosmochimica Acta* 50: 1715-26.

Manzini, M., Bouvier, A.-S., Baumgartner, L. P., Müntener, O., Rose-Koga, E. F., Schiano, P., Escrig, S., Meibom, A., and Shimizu, N. 2017. Weekly to Monthly Time Scale of Melt Inclusion Entrapment Prior to Eruption Recorded by Phosphorus Distribution in Olivine from Mid-Ocean Ridges. *Geology* 45: 1059-62.

Marrocchi, Y., Villeneuve, J., Batanova, V., Piani, L., and Jacquet, E. 2018. Oxygen Isotopic Diversity of Chondrule Precursors and the Nebular Origin of Chondrules. *Earth and Planetary Science Letters* 496: 132-41.

McSween, H. Y. Jr. 1977. Carbonaceous Chondrites of the Ormans Type: A Metamorphic Sequence. *Geochimica et Cosmochimica Acta* 41: 477-91.

McSween, H. Y. Jr., and Huss, G. R. 2010. *Cosmochemistry. Contemporary Physics*. Cambridge University Press 52: 484. https://doi.org/10.1080/00107514.2011.580055

Milman-Barris, M., Beckett, J., Baker, M., Hofmann, A., Morgan, Z., Crowley, M., Vielzeuf, D., and Stolper, E. 2008. Zoning of Phosphorus in Igneous Olivine. *Contributions to Mineralogy and Petrology* 155: 739-65.

Mourey, A. J., and Shea, T. 2019. Forming Olivine Phenocrysts in Basalt: A 3D Characterization of Growth Rates in Laboratory Experiments. *Frontiers in Earth Science* 7: 300.

Nagahara, H., Kita, N. T., Ozawa, K., and Morishita, Y. 2009. Condensation of Major Elements During Chondrule Formation and Its Implication to the Origin of Chondrules. *Geochimica et Cosmochimica Acta* 72: 1442-65.

Olsen, E., and Grossman, L. 1978. On the Origin of Isolated Olivine Grains in Type 3 Carbonaceous Chondrites. *Earth and Planetary Science Letters* 41: 111-27.

Radomsky, P. M., and Hewins, R. H. 1990. Formation Conditions of Pyroxene-Olivine and Magnesian Olivine Chondrules. *Geochimica et Cosmochimica Acta* 54: 3475-90.

Richardson, S. M., and McSween, H. Y. Jr. 1978. Textural Evidence Bearing on the Origin of Isolated Olivine Crystals in C2 Carbonaceous Chondrites. *Earth and Planetary Science Letters* 37: 485-91.

Roedder, E. 1981. Significance of Ca-Al-Rich Silicate Melt Inclusions in Olivine Crystals from the Murchison Type II Carbonaceous Chondrite. *Bulletin of Mineral Research* 104: 339-53.

Rubin, A. E. 2004. Aluminian Low-Ca Pyroxene in a Ca-Al-Rich Chondrule from the Semarkona Meteorite. *American Mineralogist* 89: 867-72.

Salas, P., Ruprecht, P., Hernández, L., and Rabbia, O. 2021. Out-of-Sequence Skeletal Growth Causing Oscillatory Zoning in Arc Olivines. *Nature Communications* 12: 4069.

Scott, E. R. D., and Krot, A. N. 2014. Treatise on Geochemistry. In *Reference Module in Earth Systems and Environmental Sciences*, edited by K. K. Turekian, and H. D. Holland, 2nd ed., vol. 1, 65-137. Amsterdam: Elsevier.

Sears, D. W., Huang, S., and Benoit, P. H. 1996. Open-System Behaviour During Chondrule Formation, edited by R. H. Hewins, R. H. Jones, and E. R. D. Scott, 221-31. *International Conference: Chondrules and the Protoplanetary Disk*. Cambridge: Cambridge University Press.

Shea, T., Hammer, J. E., Hellebrand, E., Mourey, A. J., Costa, F., First, E., Kendra, J. L., and Melnik, O. 2019. Phosphorus and Aluminum Zoning in Olivine: Contrasting Behavior of Two Nominally Incompatible Trace Elements. *Contributions to Mineralogy and Petrology* 174: 85.

Steele, I. M. 1986. Compositions and Textures of Relic Forsterite in Carbonaceous and Unequilibrated Ordinary Chondrites. *Geochimica et Cosmochimica Acta* 50: 1379-95.

Sunagawa, I. 1981. Characteristics of Crystal Growth in Nature As Seen from the Morphology of Mineral Crystals. *Bulletin of Mineral Research* 104: 81-7.

Tissandier, L., Libourel, G., and Robert, F. 2002. Gas-Melt Interactions and Their Bearing on Chondrule Formation. *Meteoritics & Planetary Science* 37: 1377-89.

Tsuchiyama, A. 1983. Crystallization Kinetics in the System CaMgSi₂O₆-CaAl₂Si₂O₈: The Delay in Nucleation of Diopside and Anothite. *American Mineralogist* 68: 687-98.

Tsuchiyama, A., and Nagahara, H. 1981. Effects of Precooling Thermal History and Cooling Rate on the Texture of Chondrules: A Preliminary Report. *Memoirs of National Institute of Polar Research* 20: 175-92.

Tsuchiyama, A., Osada, Y., Nakano, T., and Uesugi, K. 2004. Experimental Reproduction of Classic Barred Olivine Chondrules: Open-System Behavior of Chondrule Formation. *Geochimica et Cosmochimica Acta* 68: 653-72.

Varela, M. E., Kurat, G., Hoppe, P., and Brandstätter, F. 2002. Chemistry of Glass Inclusions in Olivines of the CR Chondrite Renazzo, Acfer 182, and El Djouf 001. *Geochimica et Cosmochimica Acta* 66: 1663-79.

Varela, M. E., Kurat, G., and Zinner, E. 2006. The Primary Liquid Condensation Model and the Origin of Barred Olivine Chondrules. *Icarus* 184: 344-64.

Vetere, F., Iezzi, G., Behrens, H., Cavallo, A., Misiti, V., Dietrich, M., Knipping, J., Ventura, G., and Mollo, S. 2013. Intrinsic Solidification Behavior of Basaltic to Rhyolitic Melts: A Cooling Rate Experimental Study. *Chemical Geology* 354: 233-42.

Vetere, F., Iezzi, G., Behrens, H., Holtz, F., Ventura, G., Misiti, V., Cavallo, A., Mollo, S., and Dietrich, M. 2015. Glass Forming Ability and Crystallization Behavior of Sub-Alkaline Silicate Melts. *Earth Science Reviews* 150: 25-44.

Walker, D., Kirkpatrick, R. J., Longhi, J., and Hays, J. F. 1976. Crystallization History of Lunar Picritic Basalt Sample 12002: Phase-Equilibria and Cooling Rate Studies. *Geological Society of America Bulletin* 87: 646-56.

Weinbruch, S., Palme, H., and Spettel, B. 2000. Refractory Forsterite in Primitive Meteorites: Condensates from the Solar Nebular? *Meteoritics & Planetary Science* 35: 161-71.

Welsch, B., Faure, F., Bachèlery, P., and Famin, V. 2009. Microcrysts Record Transient Convection At Piton de la
Fournaise Volcano (La Réunion Hotspot). *Journal of Petrology* 50: 2287–305.

Welsch, B., Faure, F., Famin, V., Baronnet, A., and Bachèlery, P. 2013. Dendritic Crystallization: A Single Process for All the Texture of Olivine in Basalts? *Journal of Petrology* 54: 539–74.

Welsch, B., Hammer, J., and Hellebrand, E. 2014. Phosphorus Zoning Reveals Dendritic Architecture of Olivine. *Geology* 42: 867–70.

## SUPPORTING INFORMATION

Additional supporting information may be found in the online version of this article.

**Table S1.** Compositions (wt%) and errors associated with glasses and olivines produced in superliquidus experiments cooled at constant rate of 2 °C h⁻¹ and quenched at 1200 °C.

**Table S2.** Compositions (wt%) and errors associated with glasses and olivines produced in subliquidus experiments cooled at constant rate of 2 °C h⁻¹ and quenched at 1200 °C.

**Table S3.** Compositions (wt%) of glasses and olivines obtained with superliquidus experiment (+ΔT = 10 °C) cooled at various rates (C° h⁻¹).

Wick, M. J., and Jones, R. H. 2012. Formation Conditions of Plagioclase-Bearing Type I Chondrules in CO Chondrites: A Study of Natural Samples and Experimental Analogs. *Geochimica et Cosmochimica Acta* 98: 140–59.

Zieg, M. J., and Lofgren, G. E. 2006. An Experimental Investigation of Texture Evolution During Continuous Cooling. *Journal of Volcanology and Geothermal Research* 154: 74–88.

**Table S4.** Compositions (wt%) and errors associated with glasses and olivines produced in superliquidus experiments cooled at constant rate of 2 °C h⁻¹ and quenched at 1200 °C.

**Table S5.** Compositions (wt%) and errors associated with glasses and olivines produced in subliquidus experiments cooled at constant rate of 2 °C h⁻¹ and quenched at 1200 °C.

**Table S6.** Compositions (wt%) of glasses and olivines obtained with superliquidus experiment (+ΔT = 10 °C) cooled at various rates (C° h⁻¹).