To obtain detailed mineralogy information, the Mars Science Laboratory rover Curiosity carries CheMin, the first X-ray diffraction (XRD) instrument used on a planet other than Earth. CheMin has provided the first in situ XRD analyses of full phase assemblages on another planet

Achilles, C. N.

Bish, D. L.

Blake, D. F.

Bristow, T. F.

Chipera, S. J.

Crisp, J. A.

Des Marais, D. J.

Downs, R. T.

Farmer, J. D.

Grotzinger, J. P.

Ming, D. W.

Morookian, J. M.

Morris, R. V.

Morrison, S. M.

Rampe, E. B.

Sarrazin, P.

Treiman, A. H.

Vaniman, D. T.

Yen, A. S.

NASA Technical Reports Server

MINERALOGY BY X-RAY DIFFRACTION ON MARS: THE CHEMIN INSTRUMENT ON MARS 
SCIENCE LABORATORY.  D.T. Vaniman
1
, T.F. Bristow
2
, D.L. Bish
3
, D.W. Ming
4
, D.F. Blake
5
, R.V. Morris
4
, 
E.B. Rampe
4
, S.J. Chipera
6
, A.H. Treiman
7
, S.M. Morrison
8
, C.N. Achilles
3
, R.T. Downs
8
, J.D. Farmer
9
, J.A. 
Crisp
10
, J.M. Morookian
10
, D.J. Des Marais
5
, J.P. Grotzinger
11
, P. Sarrazin
2
, and A.S. Yen
10
. 
1
Planetary Science In-
stitute, Tucson, AZ 85719, dvaniman@psi.edu; 
2
SETI Institute, Mountain View, CA; 
3
Department of Geological 
Sciences, Indiana University, Bloomington, IN; 
4
NASA Johnson Space Center, Houston, TX; 
5
NASA Ames Re-
search Center, Moffett Field, CA; 
6
Chesapeake Energy, Oklahoma City, OK; 
7
Lunar and Planetary Institute, Hou-
ston, TX; 
8
Department of Geosciences, University of Arizona, Tucson, AZ; 
9
School of Earth and Space Exploration, 
Arizona State University, Tempe, AZ; 
10
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, 
CA; 
11
Division of Geologic and Planetary Sciences, California Institute of Technology, Pasadena, CA. 
 
 
Introduction: To obtain detailed mineralogy in-
formation, the Mars Science Laboratory rover Curiosi-
ty carries CheMin, the first X-ray diffraction (XRD) 
instrument used on a planet other than Earth. CheMin 
has provided the first in situ XRD analyses of full 
phase assemblages on another planet. 
The CheMin Instrument: CheMin uses a Co X-
ray source, powder samples in piezo-driven vibrating 
cells, and a CCD detector in transmission geometry [1]. 
The CCD is cooled during operation and is energy-
selective, with a quick read cycle that allows single-
photon recognition and energy resolution of ~225 eV, 
sufficient to resolve diffracted Co Kα and Kβ. The 
CCD produces 2D diffraction patterns (Figure 1) that 
are processed into 1D Co Kα patterns with ~0.3° 2θ 
resolution. The 1D XRD patterns are analyzed for 
phase identification and quantification, using both 
Rietveld analysis and FULLPAT pattern fitting to cal-
culate mineral proportions [2,3; Figure 2]. 
 
 
Figure 1: Colorized 2D CCD XRD patterns of an eoli-
an sample (Rocknest) and a mudstone (John Klein). 
The region of smectite 001 diffraction, absent in Rock-
nest, is indicated in the John Klein pattern. 
 
Samples: CheMin has collected XRD data from 
three different powder samples: scoop samples from an 
eolian deposit (Rocknest) and two drill samples from a 
mudstone (John Klein and Cumberland). The mudstone 
is informally named as the Sheepbed member of the 
Yellowknife Bay formation. 
 
 
Figure 2: 1D XRD pattern of John Klein with observed 
(blue) versus calculated (red) patterns, and difference 
curve at the bottom (gray). Vertical line marks the 
smectite 001 diffraction maximum at ~10 Å. 
 
The Rocknest eolian deposit is comprised of plagi-
oclase (~An57), Fe-forsterite (~Fo62), augite, pigeon-
ite, and magnetite; minor anhydrite and quartz; and 
sanidine, hematite and ilmenite near detection limits. A 
significant amount of the sample (~30%) is X-ray 
amorphous [2]. 
The mudstone samples, John Klein and Cumber-
land, contain smectite, plagioclase (~An44), augite, 
pigeonite, Fe-forsterite (~Fo51), orthopyroxene and 
magnetite; minor sanidine, bassanite, anhydrite, akaga-
neite and pyrrhotite; and quartz, hematite, ilmenite, 
pyrite and halite near detection limits. The mudstone 
also has a significant (~30%) X-ray-amorphous com-
ponent [4]. The discussion that follows is focused on 
the mudstone mineralogy, which provides evidence for 
a potentially habitable lacustrine environment. 
Clay Mineral Characterization: Clay minerals 
were not found in the Rocknest eolian deposit but 
comprise ~20% of the mudstone samples. Despite chal-
lenges of remote operation on Mars, details about the 
clay minerals can be extracted from CheMin diffraction 
data. Typical XRD analysis of clay minerals on Earth 
can include preparation of oriented mounts, control of 
relative humidity, cation-exchange treatments, glycola-
tion, and heat treatment that are not possible on Mars. 
Moreover, the upper 2θ limit in CheMin is ~53°, pre-
cluding measurement of the 06l diffraction band (above 
70° Co Kα) for determination of trioctahedral or dioc-
1499.pdfEighth International Conference on Mars (2014)
https://ntrs.nasa.gov/search.jsp?R=20140009565 2019-08-31T20:33:11+00:00Z
tahedral character. However, the less-commonly used 
position of the maximum in the 02l two-dimensional 
diffraction band is similarly related to the b unit-cell 
parameter and can be used to distinguish trioctahedral 
(~ 22.5° Co Kα; 4.59 Å) from dioctahedral (~23.1° Co 
Kα; 4.47 Å) minerals (Figure 3). The 02l bands in both 
mudstone samples suggest turbostratic stacking and we 
interpret these clay minerals as trioctahedral smectites. 
 
 
Figure 3: Comparison of smectite 02l diffraction bands 
in John Klein and Cumberland. Minor rise at about 23 
degrees is associated with pyroxenes. 
 
The XRD pattern of John Klein has a broad 001 
peak at ~10 Å, corresponding with smectite or illite 
(Figure 2). Low K content, and a broad 001 peak with 
lack of other well-defined peaks, such as an 002 peak 
at 5 Å, argue against the presence of well-crystallized 
phyllosilicates such as mica or illite. In addition, peaks 
for kaolinite or chlorite-group minerals at 7 Å are ab-
sent. The low-angle region of the Cumberland XRD 
pattern has a second 001 peak at ~13.2 Å. This larger 
interlayer spacing in the Cumberland sample is of con-
siderable interest because complete collapse of a smec-
tite would be expected in the very dry conditions with-
in CheMin (<1% RH). Possible explanations include 
H2O retention in the interlayers by high hydration-
energy cations, such as Mg or Ca, and partial pillaring 
via incipient chloritization. These possibilities are be-
ing addressed in the lab [5] and will be addressed in the 
field as more samples are analyzed at Gale crater. 
Model of clay mineral and magnetite authigene-
sis: The 02l diffraction band maximum is very similar 
in John Klein and Cumberland and indicates a triocta-
hedral clay mineral such as ferrian saponite [6,7]. The 
mudstone has a surprisingly high abundance of magnet-
ite (~4%) for a fine-grained (<50 µm [8]) sediment. 
High magnetite content and dearth of Fe-forsterite, 
relative to other mafic minerals from basaltic sources, 
has led to a model of authigenesis with smectite and 
magnetite produced by aqueous alteration of Fe-
forsterite [4]. This model is supported by a lack of ge-
ochemical variation among the sediments of Yellow-
knife Bay relative to modal basaltic sources; such vari-
ation would be expected if the smectite and magnetite 
were transported [9]. 
Low salinity, moderate pH, and variable redox 
mineralogy: The crystalline salt content of the mud-
stone is low (<3%); moreover, when thin Ca-sulfate 
veins in the borehole walls are mapped it is clear that 
salts are concentrated in these late-diagenetic features 
and not in the mudstone matrix [4]. The salts are low-
solubility Ca-sulfates; highly soluble Mg-sulfates, and 
Fe-sulfates indicative of acidic conditions, are absent. 
Among the crystalline phases, ferrous and ferric iron 
are both present, as well as sulfides and sulfates. From 
analog studies, Fe in the mudstone smectite is likely to 
be incompletely oxidized [6,7]. XRD evidence for both 
reduced and oxidized species is supported by evolved 
gas analyses [10]. From these multiple lines of evi-
dence the mudstone has a mineral assemblage of varia-
ble redox states, moderate pH, and low salinity that 
could support a microbial community [7]. 
A post-Noachian lacustrine system: A current 
model for clay mineral occurrences on Mars relates 
them principally to the southern highlands, where they 
remain as vestiges of a wet environment that ended ~4 
Gy ago as a drier system evolved, dominated by sul-
fates rather than clay minerals [11]. The oldest sedi-
ments within Gale crater are probably of Early Hespe-
rian age [8]; data from Gale crater may thus extend the 
proposed transition from potentially habitable to less 
favorable environments to a later time. In several 
months, Curiosity will be at the central mound of Gale 
crater where abundant clay minerals have been recog-
nized from orbit [12]. Curiosity will traverse through 
the phyllosilicate stratigraphy and into overlying “dri-
er” sulfate strata. Records of a major shift in ancient 
Mars environments might be found at Gale crater. 
 
References: [1] Blake D. et al. (2012) Space Sci. 
Rev., 170, 341-399. [2] Bish D.L et al. (2013) Science, 
341, 10.1126/science.1238932. [3] Chipera S.J. and 
Bish D.L. (2002), J. Appl. Cryst., 35, 744-749. [4] 
Vaniman D.T. et al. (2014) Science, 343, 
10.1126/science.1243480. [5] Rampe E.B et al. (2014) 
45
th
 LPSC, abst. 1890. [6] Morris R.V. et al., this con-
ference. [7] Treiman et al., (in press) Am. Min. [8] 
Grotzinger J.P. et al. (2014) Science, 343, 
10.1126/science.1242777. [9] McLennan S.M. et al., 
Science, 343, 10.1126/science.1244734. [10] McAdam 
A.C. et al., this conference. [11] Bibring J.-P. et al. 
(2006) Science, 312, 400-404. [12] Milliken R.E. et al. 
(2010) GRL, 37, 10.1029/2009GL041870.  
1499.pdfEighth International Conference on Mars (2014)


Mineralogy by X-ray Diffraction on Mars: The Chemin Instrument on Mars Science Laboratory

Mineralogy by X-ray Diffraction on Mars: The Chemin Instrument on Mars Science Laboratory

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