American Mineralogist, Volume 88, pages 1703–1708, 2003

Calderonite, a new lead-iron-vanadate of the brackebuschite groupJOSÉ GONZÁLEZ DEL TÁNAGO,1,* ÁNGEL LA IGLESIA,2 JORDI RIUS,3 AND SOLEDAD FERNÁNDEZ SANTÍN1
1

Departamento de Petrología y Geoquímica, Facultad de Ciencias Geológicas, Universidad Complutense, 28040 Madrid, Spain
Instituto de Geología Económica, C.S.I.C., Facultad de Ciencias Geológicas, Universidad Complutense, 28040 Madrid, Spain
3
Institut de Ciències de Materials de Barcelona, C.S.I.C., Campus de la UAB, 01893 Bellaterra, Catalunya, Spain

2

ABSTRACTCalderonite, ideally Pb2Fe3+(VO4)2(OH), a new member of the brackebuschite group, has beenfound in the upper oxidation zone of two Pb-Zn hydrothermal deposits located at Santa Marta andAzuaga, Badajoz province, Spain. Brackebuschite and calderonite probably form a complete solid
solution, locally with important substitution of Cu and Zn for Fe and Mn. The monoclinic cell parameters derived from powder X-ray diffraction (XRD) data are: a = 7.647(5) Å, b = 6.094(1) Å, c =8.900(2) Å, b = 112.0(2)∞ and V = 384.5(4) Å3, and the six strongest lines, d-spacing (Å),(I),(hkl),––
are: 4.893(4)(011), 4.166(3)(002), 3.242(10) (211), 3.058(3)(020), 2.980(5) (103) and 2.746(5)(003).
Electron microprobe analyses (EMPA) show a certain degree of compositional variation not only
between the Santa Marta and Azuaga samples but also among grains from the same locality. A representative formula of Santa Marta calderonite, determined from EMPA, based on 9 O atoms: is(Pb1.950Ca0.004Ba0.015)1.969(Fe30+.892Cu0.059Zn0.008Al0.015)0.974 (V1.847As0.008Si0.039P0.057)1.951O7.507(OH)1.493. Fe3+ isprincipally substituted by Cu2+, and V5+ by Si4+. rc = 6.05 g/cm3. The thermogravimetric analysis yields aweight loss of 1.91%, which corresponds to the 1.493 H needed to maintain the charge balance. Differential thermal analysis shows endothermic effects at 279 and 663 ∞C due to dehydroxylation.
A single-crystal XRD refinement was carried out on a selected crystal with cationic content determined by EMPA and starting atomic positions from brackebuschite. Final R-value of 5.81% basedon 952 reflections with I > 2sI, assuming P21/m symmetry, the cell dimensions are a = 7.649 Å, b =6.101 Å, c = 8.904 Å, b = 112.23∞.
Calderonite is red orange to red brown, semitransparent to translucent with vitreous luster andred streak and powder. The fracture is splintery. Optically, it is biaxial positive, with a 2VX = 86∞ andstrong dispersion. In plane-polarized light, it is strongly pleochroic (X = light greenish brown, Y =brown, Z = reddish brown).

INTRODUCTION
The new mineral described here (calderonite) was foundduring the course of a systematic mineralogical study of themetallic deposits of the ~120 km-long Córdoba-Badajoz Shear
Zone (CBSZ) in southwestern Spain. Calderonite was found insphalerite, pyrite, galena, and minor chalcopyrite hydrothermal deposits in two localities of the CBSZ: Santa Marta andAzuaga. Electron microprobe analyses (EMPA) on this mineral show that it is a Pb-Fe vanadate with no Mn.
Calderonite is named after Professor Salvador Calderón,
1852–1911, in recognition of his important contribution to themineralogy of Spain. The mineral and the name calderonite
have been approved by the I.M.A. Commission on New Minerals and Mineral Names (IMA-CNMMN number 2001-022).
The type specimen (number MGM-7748) is kept in the Mineralogical Museum of the Instituto Geológico y Minero deEspaña, Madrid, (Spanish Geological Survey). Cotypes arepreserved in the following mineralogical museums: Príncipe* E-mail: tanago@geo.ucm.es
0003-004X/03/1112–1703$05.00

Felipe de Borbón, Escuela Técnica Superior de Ingenieros deMinas, Madrid, and Canadian Museum of Nature (number
CMNMC 83252).
Calderonite is very similar to brackebuschite, a very rare
vanadate, described from the Venus and other mines, Sierra
Gorda, Argentina (Rammelsberg 1880; Doering 1883; Foley
et al. 1997). Brackebuschite also was reported by Herman etal. (1961) from Lukunga, Zaire, but the identification is questionable because that sample has less than 100 ppm Mn andonly 0.5 to 0.1 wt% Fe. It has been also reported in Gabon andin two U.S.A. localities by Anthony et al. (2000) without available data in either of them.
Recently, we have found a new brackebuschite locality in
Almería (in southeastern Spain). This locality is situated morethan 400 km from the CBSZ and is geologically unrelated.
Occurrences
In the CBSZ, some Pb-Zn hydrothermal deposits containlate-stage V mineralizations in their upper oxidation zones.
Apalategui et al. (1985) suggested that those mineralizations
could be related to the close proximity of amphibolite bodies.

1703

1704

GONZÁLEZ DEL TÁNAGO ET AL.: CALDERONITE

The relatively high V content of minerals from Santa Marta
amphibolite bodies reinforce this hypothesis: our data indicatethat the range of V2O5 contents (in wt%) is 0.05 to 0.57 forhornblende, 1.08 to 3.53 for rutile, 0.43 to 0.57 for ilmenite,
and 0.12 to 0.17 for almandine. Late-stage tectonic movementsin the CBSZ were accompanied by hydrothermal processes.
Hydrothermal fluids likely transported V from the amphibolite
bodies to the ore oxidation zones where secondary V minerals
were formed.
In the Santa Marta and Azuaga deposits, the most common
V mineral is vanadinite. Other members of the descloizitemottramite solid solution are also present in minor amounts
and are usually observed overgrowing vanadinite. Calderonite
is the latest V mineral in the paragenesis. Its chemical weathering yields a massive product, probably amorphous, enriched in
Fe, Mn, and Zn, depleted in Pb, and with a negligible amountof V. The details of the two studied deposits and othercalderonite occurrences are given below.
Santa Marta deposit
This deposit is located 2 km NW of Santa Marta village (6∞36' E, 38∞ 37' 45 N) in Las Colmenitas and Los Llanos mine
(Muelas et al. 1977). Normally, vanadinite is the earliest V
mineral in the paragenesis, followed by descloizite showing
strong compositional differences among grains [the average Cu/(Cu + Zn) ratio is approximately 0.44]. Calderonite postdates
descloizite, and it has been found only in some cavities of thegossan zone, where the calderonite crystals locally overgrow
darker cores of descloizite. Other common secondary mineralsof the oxidation zone, not directly associated with calderonite,
are wulfenite, mimetite, cerusite, beudantite, adamite, hemimorphite, and smithsonite. Chalcophanite and native Ag areless abundant. Quartz and Ca-Fe carbonates are ubiquitous.
Santa Marta has been chosen as the type locality forcalderonite because here this mineral is more abundant than in
Azuaga. Besides, calderonite crystals from Santa Marta are of
relatively high quality and Mn free.

O8(OH). This composition is very close to that of calderonite
and far from ideal heyite (Williams 1973), which was reported
from this locality by Auer (1998).

EXPERIMENTAL METHOD
Physical and optical properties
At Santa Marta, calderonite usually occurs in empty cavities as scatteredclusters of idiomorphic crystals with maximum lengths of 1 mm. The crystals
are prismatic to tabular and show terminal faces. They normally form bundlesof parallel, striated crystals, locally flattened parallel to elongation (Fig. 1).
Individual crystals up to 250 mm are very uncommon. The crystals are semitransparent to translucent, their color is always deep red orange to red brown,
and their luster is vitreous or resinous if slightly altered. At Azuaga, thecalderonite crystals are of relatively low quality, small (<50 mm), opaque, andshow no luster. Both streak and powder of calderonite are red orange, the fracture is splintery, and the Mohs hardness lies between 3 and 4. Calderonite shows
no fluorescence under long- or short-wave ultraviolet light.
The optical angles and orientation were measured with a universal stage
using transmitted monochromatic yellow light (l = 589.3 nm). Calderonite isstrongly pleochroic with X = light greenish brown, Y = brown, and Z = reddish
brown. It is biaxial positive with a strong dispersion and 2Vx = 86∞.

Differential thermal and thermogravimetric analysis
Differential thermal analysis (DTA) and thermogravimetric analysis (TG)were carried out simultaneously with a Seiko Exstar 6000 instrument, using astatic air atmosphere and a heating rate of 10∞/min. About 15 mg of crystals
were handpicked from the Santa Marta sample, with an estimated purity of >98%.
The DTA curve for calderonite (Fig. 2) shows three endothermic effects at 279,
666, and 700 ∞C. The first and the second ones are ascribed to dehydroxylation
reactions, i.e., water removal from OH groups. The third one, an asymmetriceffect at 700 ∞C could be ascribed to one of three phenomena: melting of thesample, solid-solid phase transition, or structural collapse of the anhydrous phase.
In our opinion, melting is the most probable process because of the sharp exothermic effect observed in the cooling curve at 629 ∞C, that could be caused by thesolidification of the melt. Moreover, it was also observed that the sample was stuck
to the platinum sample-pan at the end of the run.
The TG curve shows three steps at temperature intervals 246–308, 308–
625, and 625–676 ∞C, with weight losses of 0.56, 1.35, and 0.48 wt%, respectively. The first and second ones (1.91 wt%) are ascribed to dehydroxylation
reactions, and the third one is probably caused by PbO volatilization. The sumof the first and second experimental weight losses determined for the Santa

Azuaga deposit
This deposit is situated in Azuaga, La Muda site (5∞ 47' 30
E, 38∞ 20' 20 N). Here, calderonite only appears in a few fractures cutting across altered gneisses, and it is locally associated with mottramite showing an average Cu/(Cu + Zn) ratioof 0.92. The studied calderonite and ore samples were collectedfrom the dumps at the La Muda mine by one of the authors(J.G.T.) in 1984, because there was no access to the in-situ
mineralization. Due to the limited amount and small crystal
size of the calderonite material from Azuaga, no complete characterization was possible.
Other world calderonite occurrences
Gurbanova et al. (2001) reported a mineral with a formulasimilar to calderonite from the Venus mine, Sierra Gorda, Argentina. We also have analyzed small (up to 4–5 mm) scattered
crystals from Nepomucene mine, Annaberg, Austria, where they
form a thin dark yellow crust. The chemical formula of thesecrystals, derived from a representative EMPA totaling 98.73
wt%, is (Pb1.96Ca0.02)1.98(Fe03+.97Cu0.01Zn0.12Al0.05)1.15(V1.85As0.08P0.01)1.94

FIGURE 1. Secondary electron image showing a cluster of prismatic
calderonite crystals from Santa Marta, the type locality of calderonite.

GONZÁLEZ DEL TÁNAGO ET AL.: CALDERONITE

1705

TABLE 1. Average EMPA in wt% and unit formula of calderonite
crystals from type locality Santa Marta (21 analysis)
PbO
CaO
BaO
Mn2O3
Fe2O3
CuO
ZnO
Al2O3
V 2O 5
As2O5
P 2O 5
SiO2
H 2O
Total

FIGURE 2. DTA and TG curves of calderonite from Santa Marta.

Marta sample and ascribed to water removal (1.91 wt%) agree fairly well withthe values reported by Rammelsberg (1880), 2.03 wt%, and by Doering (1883),
of 1.92 and 2.43 wt%, for brackebuschite. These are the only three H2O analyses of this mineral known at present.

Chemical composition
Several crystals and clusters were handpicked from different cavities,
mounted in epoxy, and polished. Wavelength-dispersive electron microprobe
analyses for calderonite and associated minerals were obtained using a Jeol
JXA-8900M instrument at the Universidad Complutense, Madrid. Standard
operating conditions were: accelerating voltage 20 kV, probe current 50 nA,
peak counting time 10 s and background counting time of 5 s, with a beam
diameter of 5 mm. The standards used were galena (PbMa), kaersutite (MgKa,
CaKa), benitoite (BaLa), garnet (MnKa, FeKa), chalcopyrite (CuKa), gahnite(ZnKa), albite (NaKa, AlKa), vanadinite (VKa, and Kb were used in the Tibearing amphibolite minerals), sillimanite (SiKa), fluorapatite (PKa), synthetic
AsGa (AsLa), ilmenite (TiKa), and K-feldspar (KKa). The results were processed with an on-line ZAF program.
The average composition of the Santa Marta calderonite is given in Table 1.
Concentrations of Sn, Bi, Sb, Mo, Ag, Sr, Ge, and Cd were below the detection
limit. The chemical composition of calderonite is highly variable among different grains of the same deposit, especially as far as Pb, Cu, Zn, Si, and P areconcerned. The large estimated standard deviations (Table 1) are due to the highintergranular compositional variability. Such variability has been also reported
for brackebuschite by Foley et al. (1997) and Gurbanova et al. (2001), so that it
may be a characteristic of the brackebuschite group. In the case of calderonite,back-scattered electron images locally show a weak zoning caused by small
compositional variations within the same crystal. For Santa Marta, the type locality, the average of 21 representative EMPA of different zones and crystals
yields, in combination with the H2O content determined by TG (1.91 wt%.), thefollowing unit formula based on 9 O atoms: (Pb 1.950 Ca 0.004 Ba 0.015 ) S1.968(Fe30+.892Cu0.059Zn0.008Al0.015)S0.974(V1.847Si0.039P0.057As0.008)S1.950 O7.507(OH)1.493.

Powder X-ray diffraction
The powder XRD pattern of calderonite was measured with a Phillips PW
1730 diffractometer (Bragg-Brentano geometry) with the following experimental conditions: 2q interval 2–70∞; CuKa1–2 radiation; receiving slit 0.1 mm; step
size 0.010 (∞2q); time per step 2 s, sample quantity 15 mg. Silicon powder wasused as internal standard. The peak positions were calculated with the Phillips
PC-APD software. The unit-cell parameters were refined from d-values with
the UNITCELL program (Holland and Redfern 1997). The indexed powder pattern and refined unit-cell parameters are given in Table 2. The calculated density for calderonite is 6.05 g/cm3.

Structure refinement
The data were collected with an Enraf Nonious CAD4 four-circle
diffractometer and reduced with the suite of programs included in WinGX(Farrugia 1999). Relevant data collection parameters are listed in Table 3.
Since calderonite is isostructural with brackebuschite (Fig. 3), the atomic

61.80 (1.11)
0.03 (0.02)
0.32 (0.24)<0.01 (0.00)
10.12 (0.52)
0.67 (0.34)
0.09 (0.06)
0.11 (0.10)
23.86 (0.74)
0.13 (0.47)
0.57 (0.52)
0.33 (0.27)
1.91 –
99.94

Pb
1.950
Ca
0.004
Ba
0.015
Mn
<0.001
0.892
Fe3+
Cu
0.059
Zn
0.008
Al
0.015
V
1.847
As
0.008
P
0.057
Si
0.039
H
1.493
Notes: Standard deviations are given in parentheses. H2O calculated by
TG; unit formula calculated on the basis of 9 O pfu.

TABLE 2. Indexed X-ray powder-diffraction pattern of calderonite
of Santa Marta
hkl

Iobs

dobs (Å)

001
011
–
111
002
–
201
111
–
202
–
211
020
–
103
021
003
211
–
213
022
–
221
–
300
–
312
310
–
123
301
–
223
311
–
304
–
402
–
401
131
203
–
231
–
124
312
–
115
–
324
–
422
401
322
–
125

16
43
12
34
5
18
21
100
25
48
12
48
14
15
20
5
5
11
8
9
13
3
3

8.242
4.893
4.569
4.166
3.874
3.641
3.401
3.242
3.058
2.980
2.857
2.746
2.601
2.485
2.449
2.386
2.356
2.310
2.196
2.127
2.078
2.030
1.968

dcal (Å)

8.251
4.902
4.532
4.126
3.817
3.668
3.389
3.235
3.047
2.966
2.858
2.750
2.609
2.486
2.451
2.381
2.363
2.307
2.203
2.126
2.075
2.030
1.964
1.660
7
1.900
1.908
1.881
9
1.863
1.866
1.861
10
1.793
1.793
1.792
12
1.711
1.711
8
1.689
1.690
5
1.646
1.649
6
1.615
1.617
1.613
4
1.537
1.538
4
1.524
1.524
Notes: Calculated unit-cell parameters: a = 7.647(5) Å, b = 6.094(1) Å, c
= 8.900(2) Å, a = 90∞, b = 112.0(2)∞, g = 90∞, V = 384.5(4) Å3.

1706GONZÁLEZ DEL TÁNAGO ET AL.: CALDERONITE

coordinates of brackebuschite (Foley et al. 1997) were used as starting values
for the refinement of calderonite. The refinement was carried out with SHELX93 (Sheldrick 1993). Initially, the atomic coordinates and the isotropic thermal
parameters were refined with V placed at T1 and T2, Fe at M1, and Pb at M1
and M2, using neutral form factors. The second step was the additional refinement of the occupation parameters of T1, T2, M1, M2, and M3. The third andfinal step was the additional refinement of the anisotropic thermal parameters
for all atoms. The final R values are given in Table 3 and the final atomic coordinates, the effective occupancies, and the Ueq coefficients are listed in Table 4.
Inspection of Table 4 shows that, as expected, the mean thermal vibration parameter Ueq is smaller for the O atoms of the chain (0.018 Å2) than for the rest
(0.032 Å2). Figure 3 shows a perspective view of the structure with the atomlabels. The polyhedral bond distances are listed in Table 5.
The final weighted R-value based on |F|2 with all data is 16.59%. To checkthe sensitivity of the refinement to the presence of the small cation vacancies,
an additional refinement was carried out under identical conditions but with
fixed full occupancies for the cation sites. The values of the anisotropic thermal
coefficients are in the same order, but the corresponding weighted R-value isslightly worse, having increased to 16.81%.

placed at the origin of the unit cell and linked to two different
types of tetrahedra, T1O4 and T2O4, <T1-O> and <T2-O>: 1.716
Å (4¥) and 1.702 (4¥), respectively. The two T sites are filledwith V but, for T2, both the refined mean bond length and lower
scattering power indicate a partial replacement by lighter at-

DISCUSSION
Calderonite is isostructural with brackebuschite and consists of discrete fundamental building units formed by chainsof edge-sharing M1(O,OH)6 octahedra, <M1-O>: 2.017 Å (6¥),

TABLE 3. Crystal data and relevant parameters from structure refinement of calderonite

q limits (∞)
Number of reflections
Index range

0.27 ¥ 0.07 ¥ 0.07 mm
P21/m
7.649(1)6.101(1)8.904 (1)112.23(1)384.6
Pb2 (Fe3+) (VO4)2 (OH)2
6.04
3.0 to 30.37
1259–10 < h < 10, 0 < k < 8, 0 < l < 12

Number observed reflections
Variables
MoKa radiationm (cm–1)
Tmin,Tmax,Tav
Absorption correction

952 with I > 2sI
85
0.71069 Å
47.8
0.0448, 0.0810, 0.0068
Gaussian (106920 sampling points)

R 1(all data)wR2(all data)
R 1 (I >2sI)

0.07750.16590.0581
1.037
3.8, –3.0

Dimension
Unit cell (space group)
a (Å)
b (Å)
c (Å)
b (º)
V (Å3)
Ideal formula:Z
Dcalc (g/c M3)

Goodness-of-fit (all data)
Drmax and Drmin (e/Å3)

FIGURE 3. Perspective view of the calderonite structure along theb-axis (with the c-axis across the page) showing the chains of edgesharing octahedra (Fe3+ and Cu2+) and the two different types ofsymmetry independent vanadate groups (V5+) linked to it. Single-crystal
refinement suggests that the cationic sites not belonging to the chainsof octahedra are partially empty (@2.8%). The line going from atom
O7 of the chain to atom O2 of one neighboring T1 group represents an
H bond. Sites M2 and M3 contain Pb. One of the principal differenceswith respect to the ideal brackebuschite structure is the probablepresence of a proton (@31% occupancy) bound to O6.
TABLE 5. Polyhedral bond distances in Å with e.s.d. values in parentheses
T1-O1 (2¥)
T1-O2
T1-O3
Mean:

1.707(11)1.649(17)1.799(12)
1.716

T2-O4
T2-O5 (2¥)
T2-O6
Mean:

1.675(16)1.727(10)1.679(15)1.702

M1-O3 (2¥)
M1-O5 (2¥)
M1-O7 (2¥)
Mean:

2.042(12)1.988(10)2.021(11)2.017

M2-O1 (2¥)
M2-O2
M2-O3
M2-O4
M2-O5 (2¥)
M2-O6
Mean:

2.540(11)2.739(17)3.019(12)2.607(15)2.625(10)2.826(15)2.690

M3-O1 (2¥)
M3-O1' (2¥)
M3-O4
M3-O4' (2¥)
M3-O5 (2¥)
M3-O6
M3-O7
Mean:

2.564(11)2.912(11)2.884(15)3.144(15)2.933(10)2.614(15)2.606(11)2.837

TABLE 4. Refined positional parameters and equivalent isotropic displacement parameters (in Å2) for calderonite
Site/atom
x/a
y/b
z/c
Mult.
Eff. occu.
T1 (as V)
0.5587(4)3/40.8250(3)1/2
0.977 (29)
T2 (as V)
0.9601(4)3/4
0.6621(3)1/2
0.935 (29)M1 (as Fe)
0
0
0
1/2
1.015 (28)
M2 (as Pb)–0.2614(1)3/4
0.2554(1)1/2
0.979 (23)M3 (as Pb)
0.3227(1)3/4
0.3970(1)1/2
0.958 (23)O1
0.4922(13)0.9783(18)0.7058(13)11O2
0.4525(27)3/40.9554(24)1/2
1O3
0.8084(19)3/40.9435(16)1/2
1O4
0.7295(25)3/4
0.5451(21)1/2
1O5–0.0107(14)0.0167(16)0.2193(11)11O6
0.0757(23)3/40.5350(22)1/2
1O7
0.1854(18)3/40.0808(16)1/21Notes: E.s.d. values are given in parentheses. Ueq is defined as one third of the trace of the orthogonalized Uij tensor.

Ueq0.010(1)0.009(1)0.011(7)0.0241(3)0.0312(3)0.023(2)0.040(5)0.018(3)0.035(4)0.020(2)0.029(4)0.015(3)GONZÁLEZ DEL TÁNAGO ET AL.: CALDERONITE

oms such as Si, As, and/or P. Each apical O atom, O5, of theoctahedron is bound to one T2 atom. From the remaining O
atoms of the octahedron, O3 is bound to T1, and O7 is an hydroxyl group forming an H bond with atom O2 belonging to
the T1O4 tetrahedron of a neighboring building unit (Fig. 3).
The building units are held together by the Pb atoms at sites
M2 and M3. The geometry of the eightfold-coordinated M2
site is that of a dipyramidal trigonal prism, which is typical for
Pb, <M2-O>: 2.690 Å (8¥). The environment of site M3 ismore irregular with a coordination number of eleven and, as
indicated by its lower refined scattering power, Pb in this site
is partially replaced by Ba and Ca, <M3-O>: 2.837 Å (11¥).
Comparison of the individual polyhedral distances ofcalderonite and brackebuschite (Foley et al. 1997) indicatesthat the only significant differences are in the octahedra. In
brackebuschite, the presence of Mn3+ in the octahedra causes
distortions due to the Jahn-Teller effect, observed bond lengths:
2.10(2), 1.98(2) and 1.99(2) Å. In calderonite, however, there
is no Mn3+ and, because all distances are rather similar (respective bond lengths: 2.04(1), 1.99(1) and 2.02(1) Å), no prolate
distortions of the polyhedra are found.
To determine the composition of sites T1 + T2, M1, and M2+ M3, the same crystal used for the XRD experiment was analyzed with the electron microprobe (33 sampling points). The
following relative atomic compositions were found: V(94.67%), Si (4.36%), As (0.82%), and P (0.15%) for T1 + T2;
Fe3+ (95.32%), Cu (3.35%), Zn (0.92%), and Al (0.41%) for
M1; Pb (98.72), Ba (0.92%), and Ca (0.36%) for M2 + M3.
Combination of these data with the refined effective occupancies given in Table 4 leads to the following formula for thestudied crystal:(Pb1.924Ba0.018Ca0.007)S1.949(Fe3+0.965 Cu0.034Zn0.009Al0.004)S1.012(V1.836Si0.085As0.016P0.003)S1.940O 7.506(OH)1.494
wherein 1.494 H have been introduced to preserve the chargebalance. Removal of the 1.494 H content in the form of water
represents a weight loss of 1.92%, which agrees well with theexperimental weight loss of 1.91% determined by TG. This
unit formula is similar to the previous one derived from the1707

average chemical composition and the experimental weight loss.
As already mentioned above, the interpretation of the refinement results strongly suggests that Si, As, and P are predominantly at site T2, and that Ba and Ca partially replace Pb
at M3. This result means that sites T1 and M2 are mainly occupied by V and Pb, respectively. This result also allows the cationic distribution in the unit cell to be derived and the balanceof bond valences to be calculated easily. The compositions forthe various sites are:S 0.977
S 0.963
S 1.012
S 0.979
S 0.970

T1: V0.977
T2: V0.859, Si0.085, As0.016, P0.003
M1: Fe0.965, Cu0.03, Zn0.009, Al0.004
M2: Pb0.979
M3: Pb0.945, Ba0.018, Ca0.007

The mean occupancy for the sites other than M1 is 0.972(7),and the small dispersion about this value is noteworthy. Thebalance of valence bond sums for this specific metal distribution is illustrated in Table 6. Inspection of those results demonstrates the plausibility of the refined crystal structure and, in
addition, illustrates the distribution of H atoms needed toachieve the formal charge of the O atoms. This situation can besummarized in three points: (1) As already known frombrackebuschite, hydroxyl O7-H contributes approximately 0.26
v.u. (valence units) to the bond strength of atom O2 (distance
O7...O2 = 2.67 Å). (2) Atom O6 of T2O4 has a charge deficit
compensated by 0.31 H. As no close contacts exist to other O
atoms, O6-H forms no H bonds [closest contact: O6...O5 =3.10Å (2¥)]. (3) A second H bond (with only 11% occupation)of type O4-H...O1 (distance O4...O1 = 2.78 Å) seems to exist
that would be related to the substitution of V5+ by of Si4+ in the
T2O4 groups.

BRACKEBUSCHITE-CALDERONITE: THE MN3+ - FE3+
END-MEMBERS OF A COMPLETE SOLID SOLUTION?
Foley et al. (1997) found two brackebuschite types: one
richer in Fe and the other one richer in Mn. They found that

TABLE 6. Balance of bond valences for calderonite calculated according to the logarithmic expression L(v) = L(1)corr – 2k log v, with
L(1)cor r= L(1) + 2k log(Svideal/Svreal), (Allmann 1975)
Atom
O1
1

/2O2

1

/2O3

1

/2O4

1

/2T1
1.707
1.24
1.649
1.47
1.799
0.94

1

/2T2

1.675
1.28
1.727
1.10
1.679
1.26

1
/2 M1
2.540
0.34
2.739
0.20
2.042 (2¥)
0.47

1
/2M2
2.564, 2.912
0.31, 0.13

1

/2 M3
2.02

SC V

1.67
3.019
0.10
2.607
0.28
2.625
0.27
2.826
0.16

H
2.02

SC Vcorr

1.93
+.26
1.98

1.98

2.884, 3.144(2¥)
1.84
1.93
0.14, 0.07(+.09)
O5
1.988
2.933
2.03
2.03
0.54
0.12
1
/2O6
2.614
1.69
2.00
0.27
(+.31)
1/2O7
2.021 (2¥)
2.606
1.26
2.00
0.49
0.28
+.74
SA V
4.885
4.730
2.907
1.958
1.946
SH 1.40
CN
4
4
6
8
11
2k
0.78
0.78
0.88
0.90
0.90
Notes: Site compositions: T1 = V0.977; T2 = V0.859, Si0.085, As0.016, P0.003; M1 = Fe0.965, Cu0.034, Zn0.009, Al0.004; M2 = Pb0.979; M3 = Pb0.979, Ba0.018, Ca0.007.
Upper values = distances in Å; lower values = bond valences. The bond valences due to the H atoms not present in the ideal brackebuschite
structure are given in parentheses. Distances O7…O2 = 2.67(2) Å; O1...O4 = 2.78(2) Å; CN = coordination number of the respective polyhedra.

1708GONZÁLEZ DEL TÁNAGO ET AL.: CALDERONITE

group, which consists of čechite, pyrobelonite, descloizite, andmottramite.

ACKNOWLEDGMENTS
F. Gordillo (1996) found the calderonite mineralization in the Santa Marta
mine and provided us with the specimens that were investigated. B. Sainz deBaranda suggested that it could be a new mineral, and supplied the Nepomucene
mine specimen. We thank A. Fernández Larios of the Centro de Microscopía
Electrónica of the Universidad Complutense for kindly using his analytical experience to obtain best-possible EMPA, and the beautiful SEM images. We thank
C. Rosi and J. Abati for their assistance with the English translation and, finally,
L.A. Groat and an anonymous reviewer for improving the manuscript. The Spanish MCyT and European FEDER, project no. MAT2002-02808, for financial
support (J. Rius).

REFERENCES CITEDF IGURE 4. Variation of Fe, Mn, Cu-Zn content in known
calderonites and brackebuschites. Calderonite: Badajoz, filledtriangles; Annaberg, filled circle. Brackebuschite from Sierra Gorda,
Argentina: open star, Rammelsberg (1880); plus signs, Doering (1883);
open diamonds, Symes and Williams (1973); filled stars, Foley et al.
(1997); open circle, Gurbanova et al. (2001); Brackebuschite from
Almería, Spain: open inverted triangles. All analyses have beennormalized to one OH group, and with all Fe and Mn as Fe3+ and Mn3+.

Mn-rich and Fe-rich regions may coexist even in the same crystal. Due to their similar atomic radii (Mn3+ = 0.58 Å and Fe3+ =0.55 Å), the geochemical behavior of Mn3+ and Fe3+ are very
close. A ternary Fe-Mn-(Cu + Zn) plot including all calderonite
and brackebuschite compositions known to date is shown in
Figure 4. The composition was renormalized by recalculating
Mn and Fe as Mn3+ and Fe3+, and H2O, was inferred from bystoichiometry. The Doering (1883) analyses yield: Pb1.90-1.87(Mn30+.48–0.57Fe30+.46–0.51Cu0.04Zn0.11)(V1.93–1.96P0.02)O8(OH).
As suggested in Figure 4, brackebuschite and calderonite
probably form a solid solution with no compositional gap. These
two minerals, along with other Cu-dominated and Zn-dominated members yet to be discovered, might constitute abrackebuschite group of minerals, similar to the descloizite

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MANUSCRIPT RECEIVED AUGUST 15, 2002
MANUSCRIPT ACCEPTED MAY 22, 2003
MANUSCRIPT HANDLED BY ALESSANDRO GUALTIERI