Mechanical Properties of Simulated Mars Materials—

Gypsum-Rich Sandstones and Lapilli Tuff

U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2013–1242
Mechanical Properties of Simulated Mars Materials—

Gypsum-Rich Sandstones and Lapilli Tuff

By Carolyn Morrow, David Lockner, and Chris Okubo

Open-File Report 2013–1242

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013

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Suggested citation:

Morrow, C., Lockner, D., and Okubo, C., 2013, Mechanical properties of simulated Mars materials—Gypsum-rich 

sandstones and lapilli tuff: U.S. Geological Survey Open-File Report 2013–1242, 11 p., 

http://dx.doi.org/10.3133/ofr20131242.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

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materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright 

owner.
iii

Contents

Introduction ....................................................................................................................................................................1

Sample Preparation .......................................................................................................................................................1

Experimental Procedure.................................................................................................................................................2

Axial Deformation Tests .............................................................................................................................................2

Hydrostatic Tests........................................................................................................................................................3

Strain Calculations..................................................................................................................................................3

Results and Discussion..................................................................................................................................................4

Conclusions....................................................................................................................................................................6

References.....................................................................................................................................................................7

Figures ...........................................................................................................................................................................8

Figures

Figure 1. Differential stress as a function of axial displacement for A, 100-series samples; B, 200-series samples;

C, 300-series samples; and D, lapilli tuff. ..........................................................................................................8

Figure 2. Volumetric strain as a function of effective pressure for the four sample types. .............................................9

Figure 3. Mean effective stress as a function of porosity change for both deformation tests and hydrostatic

loading of the 100 series samples.....................................................................................................................9

Figure 4. Young’s Modulus as a function of effective pressure for three sample types. ..............................................10

Figure 5. Poisson’s Ratio for selected 300 series and lapilli tuff samples....................................................................10

Figure 6. Bulk Modulus of the four sample types as a function of the average effective pressure during the

measurement. .................................................................................................................................................11

Tables

Table 1. Physical Properties of Samples ....................................................................................................................6
Mechanical Properties of Simulated Mars Materials: 

Gypsum-Rich Sandstones and Lapilli Tuff

By C. Morrow, D. Lockner, and C. Okubo

Introduction

Observations by the Mars Exploration Rover (MER) Opportunity, and other recent studies on 

diagenesis in the extensive equatorial layered deposits on Mars, suggest that the likely lithologies of 

these deposits are gypsum-rich sandstones and tuffaceous sediments (for example, Murchie and others, 

2009; Squyres and others, 2012; Zimbelman and Scheidt, 2012). Of particular interest is how the 

diagenesis history of these sediments (degree of cementation and composition) influences the strength

and brittle behavior of the material. For instance, fractures are more common in lower porosity materials 

under strain, whereas deformation bands, characterized by distributed strain throughout a broader 

discontinuity in a material, are common in higher porosity sedimentary materials. Such discontinuities 

can either enhance or restrict fluid flow; hence, failure mode plays an important role in determining the 

mechanics of fluid migration through sediments (Antonellini and Aydin, 1994; 1995; Taylor and 

Pollard, 2000; Ogilvie and Glover, 2001). As part of a larger study to characterize processes of faultcontrolled fluid flow in volcaniclastic and gypsum-rich sediments on Mars, we have completed a series 

of laboratory experiments to focus on how gypsum clast content and degree of authigenic cementation 

affects the strength behavior of simulated Mars rocks. Both axial deformation and hydrostatic pressure 

tests were done at room temperature under dry conditions.

Sample Preparation

Four types of simulated Mars materials were tested. These materials include three variations on a 

gypsum mixture to simulate Martian sandstone and a terrestrial lapilli tuff to substitute as a Martian 

tuffaceous sediment. The gypsum mixtures were identified as:

• 100 series: 80 percent gypsum sand, 20 percent calcium sulfate hemihydrate,

• 200 series: 50 percent gypsum sand, 50 percent calcium sulfate hemihydrate, and

• 300 series: 15–25 percent gypsum sand, 25–35 percent basalt sand, 50 percent calcium sulfate 

hemihydrate.

Percentages are by weight as measured before reacting with water. The gypsum sand was 

collected from the active dune field in White Sands National Monument, New Mexico. The sand was 

dried to ambient humidity (~40 percent RH), and the entire sample batch, ~19 L, was homogenized by 

mixing. The sample was passed through a 1 mm sieve, and only grains smaller than 1 mm in diameter 

were used to prepare the samples.

The basalt sand was prepared by pulverizing basalt using a hammer drill. The sample is from the 

basalt of Switzer Mesa, part of the San Francisco volcanic field in northern Arizona. This flow is recent, 

5.82±0.34 Ma (Damon and others, 1974), and minimally weathered. Identical to the gypsum sand, the 

basalt sand was dried to ambient humidity (~40 percent RH), and the entire sample batch, ~2 L, was 
2

homogenized by mixing. The sample was passed through a 0.109 mm sieve, and only grains smaller 

than 0.109 mm in diameter were used to prepare the samples.

Samples were prepared by thoroughly mixing the gypsum sand, calcium sulfate hemihydrate 

powder, and basalt sand (if any). The mixture was passed through the 1 mm sieve twice during mixing 

in order to disaggregate the calcium sulfate hemihydrate powder and basalt sand. The sample mixture 

was then poured into a 25.4 mm ID, 3.2- mm-walled latex tube at increments of 9 cm3, and the sample 

was compressed to 1 MPa after each increment was added. Additionally, 5 mL of deionized water was 

added into the latex tube after each sample increment was added and compressed. The water absorbed 

quickly into the gypsum mixture. This process was repeated until the sample reached a column length of 

63.5 mm. Thin Berea sandstone frits (20 percent porosity) were inserted on either end of the gypsum 

mix for stability and to act as pore fluid-permeable caps. The entire sample was submerged in roomtemperature deionized water for one hour, then air dried for at least one week. We refer to the resulting 

simulated rock as a “gypsum sandstone” based on grain size rather than mineralogy.

The lapilli tuff is from the northeast flank of North Menan Butte, which is part of the Menan 

Volcanic Complex in the Snake River Plain, eastern Idaho. Because the samples were too friable to be 

cored into cylinders, matching the geometry of the gypsum-rich samples, they were straight cut into 

prisms of roughly 19 by 19 mm square and 63.5 mm long. Thin, square wafers of Berea sandstone were 

placed on either end to ensure uniform distribution of the pore-pressure medium through the lapilli tuff. 

This rock sandwich was then held in placed between two stainless-steel adaptors with thin shrink tubing, 

and the entire assembly was then inserted into a length of latex tubing. The adaptors are shaped to 

transfer stress from the square cross-sectional rock to the round cross-sectional loading piston.

Experimental Procedure

Axial Deformation Tests

Because Martian sediments in the equatorial layered deposits currently are dry, all our simulated 

samples (in their latex jackets) were vacuum dried overnight at 50 °C to ensure a dry state. They were 

then attached to stainless-steel endplugs with a pore pressure inlet at the top. This assembly was tested in 

a standard triaxial apparatus at room temperature and effective stress, Pe (defined as confining pressure, 

Pc, minus pore pressure, Pp) of 2, 5, 10 and 15 MPa. A constant pore pressure of Pp=10 MPa argon gas 

was applied in all tests so that the samples remained dry at all times. The argon gas was contained in a 

closed system comprised of the sample, tubing, and computer-controlled pore-pressure generator. By

assuming that the change in the sample matrix material is small compared to the change in pore volume, 

pore volume change can be determined by recording the volume change in the pore-pressure generator 

required to maintain constant pressure. At constant pore pressure, there is no correction required for the 

compressibility of argon in the volume measurements. Room temperature was controlled to ±0.2 degrees 

Celsius to minimize errors in pore volume due to thermal expansion of the argon gas.

The gypsum samples were deformed to 10 mm axial shortening at a rate of 0.000635 mm s-1

(equivalent to 0.001 mm s-1 along a 30° inclined fault plane). Lapilli tuff samples were deformed to 8 

mm axial shortening at the same rate. In most tests, the direction of the piston was reversed during the 

initial loading for a short time, causing stresses to drop, then reversed again to resume loading the 

sample. Initial application of axial stress results in a combination of elastic and inelastic sample 

shortening. Young’s modulus depends on only the elastic strain resulting from a stress change. To 

isolate elastic strain, axial stress must be cycled a second time, following the initial loading. A greased 

Teflon shim, placed between the piston and the sample assembly, allowed easy lateral slip of the lower 

portion of the sample (if necessary) during deformation. Axial load was measured with an internal load 

cell. Because the load cell is calibrated to provide stress on a 25.4-mm diameter piston, axial load values 

of the rectangular lapilli tuff samples were adjusted by the ratio of the cross-sectional area of the 
3

samples to that of the piston. Axial shortening, confining pressure, and pore pressure were all measured 

at 1 sample s

-1

. The axial stress, confining pressure, and pore pressure have an accuracy of at least 0.03 

MPa.

Hydrostatic Tests

A separate series of tests was done on the four sample types under hydrostatic loading (no piston 

contact), with samples prepared as above. Effective pressure was increased slowly from 1 MPa to values 

between 40 and 100 MPa, (depending on sample behavior), while pore pressure was maintained at 10 

MPa. Pore volume change in the sample was determined by recording the volume change in the pressure 

generator, as described above. Effective pressure cycling was done during these experiments to 

determine the bulk modulus of the samples.

Strain Calculations

Axial, volumetric, and transverse strain calculations are necessary to determine the physical 

constants of the rocks. We compute axial strain, εax, from the axial displacement measurement as 

follows. Axial strain is defined as

 εax = ∆L/L, (1)

where L is sample length. However, axial displacement, ∆z, measured outside of the pressure vessel, 

includes both sample shortening, ∆L, and piston/machine shortening, ∆zm. The piston/machine 

shortening is characterized by the machine stiffness Km and is determined in separate calibration tests on 

a steel sample according to

 ∆σ1 = Km ∆zm, (2)

where σ1 is axial stress. Then

 εax = (∆z - ∆σ1/Km)/L. (3)

Axial displacement can be measured to ±0.5 micron, however, owing to the nature of the sample 

fabrication technique, the sample length can be measured only to ±0.5 mm. Consequently, changes in 

axial strain during a single experiment are known to a precision of 10-5,

while absolute strain is only 

known to about ±2 percent.

Young’s modulus, Ey=∆σ1/∆εax, is computed from the slope of an axial stress versus 

displacement plot as stress is cycled during elastic loading. The slope of the curve (in MPa/mm) gives 

the composite sample/machine stiffness, Ktotal = ∆σ1 /∆z. Rearranging (3) and substituting for ∆z gives

 Ktotal = ∆σ1/(∆εax L + ∆σ1/Km). (4)

Rearranging terms leads to the expression for Young's modulus:

 Ey = L(1/Ktotal - 1/Km)

-1

. (5)

Porosity, φ, is given by

 φ = (Vpo + ∆Vp)/(Vo + ∆Vp), (6)

where Vpo is the initial pore volume, ∆Vp is the change in pore volume, and Vo is the initial total sample 

volume. Assuming that the change in matrix volume is insignificant, we can express volumetric strain as 

εvol =φ - φo, where φo is initial porosity. Because we do not know the initial porosity of these samples, we 

only relate changes in volumetric strain. Pore volume change can be measured to ±0.0005 cc. However, 

because of uncertainty in the total sample volume, we estimate the volumetric strain accuracy to be ±2 

percent.
4

Finally, since

 εvol = 2εtr + εax (7)

where εtr is the transverse strain, we obtain Poisson’s ratio, ν=-εtr/εax from the relation

 ν = (1 - εvol /εax)/2. (8)

Results and Discussion

Differential stress (σ∆=σ1-Pc) as a function of axial displacement for the four sample types is 

shown in figure 1A–D. Differential stress increased with effective pressure in all cases as expected. The 

100-series samples were the weakest of the gypsum sandstones because of the lesser percentage of 

cementing material. There was no discernable elastic portion of these deformation curves, that is, grain 

crushing and pore collapse occurred from the onset of loading. The 200- and 300-series samples were 

similar in strength, although 200-series samples were stiffer during the elastic portions of the curves, 

indicating a higher Young’s modulus than the 300-series samples. Many of the gypsum sandstone

samples showed quasi-stable stress drops of up to 2 MPa during deformation that were neither dynamic 

nor audible. These events had durations of a fraction of a second to a few seconds and may represent 

discrete compaction events. Some of the 200- and 300- series samples exhibited a peak differential stress 

with subsequent weakening, and in some cases, an eventual strength recovery at larger displacements. In 

contrast, the lapilli tuff samples all exhibited stable deformation, with smooth differential stress curves 

during axial shortening. The large stress drops occurring at 5, 10, and 15 MPa were imposed to measure 

Young’s modulus and should not be misinterpreted as stick-slip events.

All samples were examined after removal from the pressure vessel. The 100-series samples 

showed no visible fractures, with no barreling along the length of the sandstone cylinders in most cases. 

The sample at 10 MPa showed a 2 percent increase in the diameter at the center of the sample. The 200-

and 300-series samples were both characterized by discrete fractures in almost every case, all at 30 

degrees ±2 degrees from the axis of the rock cylinder. At 15 MPa, the 200-series sample showed a 7 

percent increase in diameter at the center (barrel) rather than a fracture. Axial stress values were not 

corrected for barreling, that is, axial stresses were computed assuming a 25.4-mm- diameter sample 

cross-section. We did not observe a trend of fault formation transitioning to compaction failure as a 

function of increasing effective pressure. More experiments would be needed to identify such a 

correlation. None of the lapilli tuff samples showed evidence of fracturing or barreling after 

pressurization. These samples deformed by crushing and pore collapse. Compaction bands would be 

hard to discern along the sides of any of these sample types, so we do not report on them here.

Changes in volumetric strain, calculated from the hydrostatic tests are shown in figure 2.

Negative volumetric strain corresponds to decreasing sample volume, that is, the sample expelled argon 

gas. The gypsum sandstones show a more complex response to pressure than the lapilli tuff, with a 

shoulder to the strain curves at various effective pressures. The lapilli tuff is characterized by steadily 

decreasing rate of strain with pressure. Hysteresis loops during volumetric strain correspond to the 

effective pressure cycles used to measure bulk modulus. Because bulk modulus is a function of effective 

pressure, the pressure cycles were all performed in a similar pressure range (Pe<25 MPa) for a better 

comparison. After removal from the pressure vessel, all four sample types had a uniform exterior 

appearance, with no indication of discrete fracture formation.

An effort was made to differentiate between Mohr-Coulomb failure and shear- enhanced 

compaction following the procedure of Wong and Baud (1999) by characterizing the Q/P strength 

envelope of the materials. We start by plotting mean effective stress versus porosity change for both the 

deformation and hydrostatic tests (fig. 3) and then pick off points where the deformation tests diverge 

from the hydrostatic curve, designated as the critical stress states C* (for compaction) or C’ (for 
5

dilation) (see Wong and Baud, 1999). At the two highest pressures of the 100-series samples, the 

deformation tests diverged immediately rather than following the hydrostatic curve during initial 

loading. That is, the samples immediately failed at a rate faster than predicted from hydrostatic loading 

tests, by shear-enhanced compaction, due to their weak cementation as observed in figure 1A. At 2 MPa, 

the reversal in direction along the porosity change axis indicated that the sample had started to compact, 

and then with further deformation, began to dilate. This behavior is common where effective pressures 

are low enough that the sandstone grains can ride over one another, causing a volume expansion, rather 

than deform by grain crushing and porosity loss alone. The equivalent plots for the 200-series, 300-

series, and lapilli tuff samples were not as systematic and did not follow the trend of the hydrostatic 

curves during initial loading. However, dilation was observed at the lower pressures and compaction 

was observed at higher pressures for all three sample types. More extensive tests, including detailed 

microstructural analysis, would be needed to properly distinguish differences in micromechanical 

deformation mode in these samples.

Nonetheless, physical properties of the samples are straightforward to calculate. For instance, 

Young’s modulus, Ey, is shown for the 200-series, 300-series, and lapilli tuff samples in figure 4. (The 

100-series samples were not pressure cycled, so Young’s modulus could not be determined). Young’s 

modulus values in figure 4 generally increased linearly with effective pressure, and all fell within the 

range of 2,000–9,000 MPa. The 200-series samples had distinctly higher values of Ey than the 300-series 

samples, showing that the addition of basaltic dust to the 300-series samples lowered the modulus 

considerably, even though both series had similar pressure dependence (∆Ey/∆Pe) of 340–350 MPa per 

MPa effective pressure (note the parallel trend lines). Lapilli tuff samples had the lowest Young’s 

modulus and exhibited less pressure sensitivity of Ey, at 197 MPa per MPa effective pressure. Error bars 

in figure 4 are ±5%.

Four of the experiments lent themselves to calculations of Poisson’s ratio—two series 300 

samples and two lapilli tuff samples (fig. 5). Poisson’s ratio is a measure of the lateral expansion of a 

material from a given lengthwise compression. Values ranged from 0.18 to 0.29. Error bars indicate 

1σ values in figure 5. Poisson’s ratio measurements would be possible on the complete suite of samples 

if the experiments were done at a slower deformation rate, so that pore-volume response (requiring 

argon to diffuse in or out of the sample) was better linked to the changing stresses.

Bulk modulus (fig. 6) was calculated from the volume response during the pressure cycle loops 

of the hydrostatic tests shown in figure 2. During the reloading of pressure, we determined the slope of 

the volumetric strain versus effective pressure. Bulk modulus is the inverse of this number. In figure 6, 

values are plotted at the mean effective pressure during the pressure cycle. Bulk modulus was variable, 

ranging from around 2,500 to 4,500 MPa for the four sample types. The 100-series sample (low 

cementation) had the lowest value, whereas the 200-series sample (more cementation and no basaltic 

dust), had a considerably higher value than all the others. The addition of basaltic dust may be a factor in 

the 300-series value compared to the 200-series value (as well as the difference in effective pressure). 

Error bars (±2%) are smaller than the data points. Data for all the physical properties plotted in figures 

4–6 can be found in table 1.
6

Table 1. Physical Properties of Samples

Series Pe* (MPa) Young’s Modulus 

(Ey, MPa) Poisson’s Ratio, ν Bulk Modulus (MPa)

100 13-25 2470

200 2 4460

200 5 6160

200 10 9000

200 15 8650

200 16–22 4440

300 2 3440

300 5 3940

300 10 6230 0.27 ± 0.04

300 15 7770 0.29 ± 0.07

300 4–11 2970

tuff 5 2120

tuff 10 3130 0.28 ± 0.06

tuff 15 4090 0.18 ± 0.06

tuff 12–19 3100

*Bulk Modulus was measured over a range of pressures.

Conclusions

We have measured the strength of simulated Mars materials under a range of pressure conditions 

in a dry state. Strength increased with increasing effective confining pressure in all cases. Several types 

of deformation behavior were observed, including stable sliding and repeated, small, quasi-stable stress 

drops. The 100-series samples showed shear-enhanced compaction as soon as deviatoric stress was 

applied, owing to their low degree of cementation. All the gypsum-rich sandstones were comparatively 

weak relative to silica-rich sandstone types (for example, Wong and others, 1997), because gypsum is 

inherently weaker than quartz. Peak differential stress was generally less than 40 MPa even after 10 mm 

of axial shortening. Like the 100-series samples, the lapilli tuff samples run at higher effective pressures, 

continued to strain harden for the entire experiment, and never reached a steady strength. In all cases, it 

was difficult to differentiate between Mohr-Coulomb failure and shear-enhanced compaction following 

the procedure of Wong and Baud, 1999, although discrete failure planes, all at 30 degrees ±2 degrees, 

were apparent in many of the 200- and 300-series samples.

Physical properties such as Young’s modulus, Poisson’s ratio, and bulk modulus, were readily 

obtainable and reflected the nature of these weak gypsum-rich sandstones and volcaniclastic rocks (see, 

for example, Lama and Vutukuri, 1978, for a comparison of other rock types). Young’s modulus was 

dependent on composition, and increased linearly with effective confining pressure. Values ranged from 

2,000 to 9,000 MPa for the four sample types over the pressure range tested. Poisson’s ratio, measured 

for the 300-series sandstones and the lapilli tuff, ranged from 0.18 to 0.29. The bulk modulus of the four 

samples, measured at effective confining pressures below 20 MPa, ranged from 2,470 to 4,440 MPa.
7

References

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petrophysical properties: American Association of Petroleum Geologists Bulletin, v. 78, p. 355–377.

Antonellini, M., and Aydin, A., 1995, Effect of faulting on fluid flow in porous sandstones; geometry 

and special distribution: American Association of Petroleum Geologists Bulletin, v. 79, p. 642–671.

Damon, P.E., Shafiqullah, M., and Leventhal, J.S., 1974, K-Ar chronology for the San Francisco 

volcanic field and rate of erosion of the Little Colorado River, in Karlstrom, T.N.V., Swann, G.A., and 

Eastwood, R.L., eds., Geology of northern Arizona, Part I—Regional studies: Geological Society of 

America, Rocky Mountain Section Meeting, Flagstaff, Ariz., Guidebook, p. 221–235.

Lama, R.D., and Vutukuri, V.S., 1978, Handbook on mechanical properties of rocks: Series on Rock and 

Soil Mechanics, v. 3, no. 1, Trans Tech Publications, Clausthal, Germany.

Murchie, S., Roach, L., Seelos, F., Milliken, R., Mustard, J., Arvidson, R., Wiseman, S., Lichtenberg, 

K., Andrews-Hanna, J., and Bishop, J., 2009, Evidence for the origin of layered deposits in Candor 

Chasma, Mars, from mineral composition and hydrologic modeling: Journal of Geophysical Research, 

v. 114, p. E00D05.

Ogilvie, S.R., and Glover, P.W.J., 2001, The petrophysical properties of deformation bands in relation to 

their microstructure: Earth Planet Science. Letters, v. 193, p. 129–142, doi:10.1016/S0012-

821X(01)00492-7.

Squyres, S.W., Arvidson, R.E., Bell, J.F., Calef, F., Clark, B.C., Cohen, B.A., Crumpler, L.A., de Souza, 

P.A., Farrand, W.H., Gellert, R., Grant, J., Herkenhoff, K.E., Hurowitz, J.A., Johnson, J.R., Jolliff, 

B.L., Knoll, A.H., Li, R., McLennan, S.M., Ming, D.W., Mittlefehldt, D.W., Parker, T.J., Paulsen, G., 

Rice, M.S., Ruff, S.W., Schröder, C., Yen, A.S., and Zacny, K., 2012, Ancient impact and aqueous 

processes at Endeavour Crater, Mars: Science, v. 336, no. 6081, p. 570–576.

Taylor, W.L., and Pollard, D.D., 2000, Estimation of in situ permeability of deformation bands in porous 

sandstone, Valley of Fire, Nevada: Water Resources. Research, v. 36, p. 2595–2606, 

doi:10.1029/2000WR900120.

Wong, T.F., David. C., and Zhu, W., 1997, The transition from brittle faulting to cataclastic flow in 

porous sandstones—Mechanical deformation: Journal of Geophysical Research, v. 102, p. 3009–3025.

Wong, T.F., and Baud, P., 1999, Mechanical compaction of porous sandstone: Oil and Gas Science and 

Technology, v. 54, no. 6, p. 715–727.

Zimbelman, J.R., and Scheidt, S.P., 2012, Hesperian age for Western Medusae Fossae Formation, Mars: 

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8

Figures 

A B 

C D 

Figure 1. Differential stress as a function of axial displacement for A, 100-series samples; B, 200-series samples; 

C, 300-series samples; and D, lapilli tuff. Effective pressures for each experiment are shown at right. Pressure 

cycling during loading in 1B–1D was conducted to determine Young’s modulus. 

0

10

20

30

40

50

0 2 4 6 8 10 12

100 Series Gypsum Sandstone

Differential Stress, MPa

Axial Displacement, mm

Pe (MPa) =

10

5

2

0

10

20

30

40

50

0 2 4 6 8 10 12

200 Series Gypsum Sandstone

Differential Stress, MPa

Axial Displacement, mm 

2

5

10

15

Pe (MPa) =

0

10

20

30

40

50

0 2 4 6 8 10 12

300 Series Gypsum Sandstone

Differential Stress, MPa

Axial Displacement, mm 

5

2

10

15

Pe (MPa) =
9

Figure 2. Volumetric strain as a function of effective pressure for the four sample types. Pressure cycling (for bulk 

modulus calculations) appears as loops. Negative slope values indicate that the sample compressed (porosity 

decreased) with applied pressure.

Figure 3. Mean effective stress as a function of porosity change for both deformation tests and hydrostatic loading 

of the 100 series samples. Porosity change (shown as positive with increasing pressure) is equivalent to the 

volumetric strain (negative with increasing pressure) shown in Figure 2.
10

Figure 4. Young’s Modulus as a function of effective pressure for three sample types. Young’s modulus was not 

tested on the 100 series samples. Error bars ±5%.

Figure 5. Poisson’s Ratio for selected 300 series and lapilli tuff samples. Poisson’s ratio is a measure of the 

lateral expansion of a material from a given lengthwise compression. Error bars ±1σ.
11

Figure 6. Bulk Modulus of the four sample types as a function of the average effective pressure during the 

measurement. Error ±2% (smaller than the data points).
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Morrow and others—Mechanical Properties of Simulated Mars Materials—Gypsum-Rich Sandstones and Lapilli Tuff—Open-File Report 2013–1242