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Workshop on Martian Phyllosilicates
Martian Phyllosilicates: Recorders of Aqueous
Processes
October 21-23, 2008; Paris, France
Discussion Summary
Jean-Pierre Bibring, David Beaty, David Bish, Janice Bishop, Jack
Mustard, Eldar Noe Dobrea, Sabine Petit, Francois Poulet, Leah
Roach
Recommended bibliographic citation
Bibring, J-P., D.W. Beaty, D. Bish, J. Bishop, J.F. Mustard, E. Noe Dobrea, S. Petit, F. Poulet, L.H. Roach, 2008, Martian
Phyllosilicates: Recorders of Aqueous Processes: Discussion Summary. Posted November, 2008 by the Institut
d'Astrophysique Spatiale (IAS) at http://www.ias.upsud.fr/Mars_Phyllosilicates/phyllo/5.%20Thursday%20morning/Phyllo_Discussion_summary.ppt
Phyllosilicates, Oct. 2008 -1
Consensus Position on Status (Oct. 2008) of
Phyllosilicate Mineral Detections on Mars
Workshop on Martian Phyllosilicates
The participants considered many possible mineral detections from
OMEGA and CRISM data. Some spectral interpretations were considered
to be distinct and well represented in the mineral libraries, while other
spectral signatures were less absolutely diagnostic of specific mineral
species. The meeting participants considered two broad classes: wellsupported mineral interpretations, and mineral identifications that needed
additional information. A partial listing of these categories follows:
Generally Accepted by Conference
Participants
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Nontronite
Al-smectite (montmorillonite,
beidellite)
Fe/Mg-smectite or sepiolite
Al-mica (illite and/or muscovite)
At least one chlorite group
mineral
At least one kaolin group mineral
More information needed
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Mixed-layer illite/smectite,
smectite/chlorite
Ca- and Na-zeolite (analcime has
been proposed)
Prehnite
Pumpellyite, epidote
Serpentine group
Phyllosilicates, Oct. 2008 -2
Phyllosilicates on Mars:
Key Questions (1 of 5)
Workshop on Martian Phyllosilicates
1 . What are the basic characteristics of the phyllosilicate
minerals on Mars?
1A. What is the range of mineralogic diversity of phyllosilicate
species on Mars?
• What are the specific species present within the larger phyllosilicate groups?
What is their crystal chemistry and ordering?
• Is there diurnal or seasonal variation in hydration state of hydrated minerals?
• Why do Mg/Fe smectites appear to dominate the spectral signatures?
• What is the variation in crystalline to poorly crystalline to amorphous forms?
• Are there “stealth” phyllosilicates or proto-phyllosilicates on Mars that are not
visible to VNIR?
• What are the conditions under which these minerals equilibrated?
1B. What are the non-phyllosilicate mineral assemblages
associated with phyllosilicate minerals on Mars?
• What are associated spectrally neutral phases (and how can we use multiple
instruments to detect them)?
• What are the paragenetic relationships?
• Why do we sometimes have many alteration minerals and other times few?
• What does the co-occurrence of sulfates tell us?
Phyllosilicates, Oct. 2008 -3
Phyllosilicates on Mars:
Key Questions (2 of 5)
Workshop on Martian Phyllosilicates
1C. What is the concentration of phyllosilicate minerals in the
different occurrences in which they have been detected?
• Are they a minor or a major component of the rocks?
• Does abundance vary by location or timing of formation?
1D. What is the range of geologic contexts in which phyllosilicate
minerals are present on Mars?
• How many different types of martian environments contain phyllosilicates?
Important progress has been made over past couple years by OMEGA and
CRISM teams, however, this work is not complete and must be continued.
• Systematic variation with lithology of primary bedrock?
• What is the relationship between cratering and phyllosilicate formation?
• Is there a difference between the shallow subsurface and the surface?
• Phyllosilicates in fans (and other sedimentary rocks) – transported or formed in
place?
• Are there systematic variations in phyllosilicate mineralogy or geologic setting as
a function of age?
• What is the relationship between the phyllosilicate-rich deposits and fluvial
networks?
• What is the absolute and relative age of phyllosilicate minerals on Mars?
Phyllosilicates, Oct. 2008 -4
Phyllosilicates on Mars:
Key Questions (3 of 5)
Workshop on Martian Phyllosilicates
1E. The orbital mineralogic detections are on a scale of 15-20m or
greater—what do the rocks and soils look like in detail?
• What are the mineralogic variations and textural relationships at a scale of 1m?
1cm? 100 mm?
• How to scale between km-scale OMEGA and cm-scale lab studies?
Phyllosilicates, Oct. 2008 -5
Phyllosilicates on Mars:
Key Questions (4 of 5)
Workshop on Martian Phyllosilicates
2. What are the genetic mechanisms by which
phyllosilicate minerals formed on Mars?
2A. What were the original formation pathways for the different
phyllosilicate minerals, and what were their subsequent
alteration pathways?
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Are terrestrial models involving granitic vs basaltic parent material adequate for
Mars? Do we need new models?
Was there a relationship between the heavy bombardment (or other cratering)
and phyllosilicate formation?
2B. Can phyllosilicate-bearing rocks be used to infer past
environmental conditions on Mars?
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Did phyllosilicates form only in the Noachian period (with subsequent
redistribution by erosion and deposition processes), and how long did this
happen? Did they also form in younger epochs? Are they forming today?
What do the phyllosilicates imply about how long liquid water was available at
the surface?
What do the clays say about the past climate?
What is the relevance of each mineral?
Phyllosilicates, Oct. 2008 -6
Phyllosilicates on Mars:
Key Questions (5 of 5)
Workshop on Martian Phyllosilicates
3. What is the relationship between the phyllosilicate
minerals observed in martian meteorites and those
detected from orbit?
– Several phyllosilicate minerals have been detected in martian
meteorites, mainly in the nakhlites. They were first detected in Nakhla in
1975, and they were just called 'iddingsite' (a general term for a mixture
of alteration minerals). The minerals are generally smectite, illite and
ferrihydrite.
4. What are the implications of phyllosilicate-bearing
rocks for the development or preservation of prebiotic chemistry and/or biosignatures?
– Were phyllosilicate minerals (especially Fe/Mg) resources for life in
some way?
– How do phyllosilicates help preserve biosignatures in the martian
environment
Phyllosilicates, Oct. 2008 -7
Phyllosilicates on Mars:
Summary of Key Questions, Oct. 2008
Workshop on Martian Phyllosilicates
1. What are the basic characteristics of the phyllosilicate minerals on
Mars?
1A. What is the range of mineralogic diversity?
1B. What are the associated non-phyllosilicate mineral assemblages?
1C. What is the concentration of phyllosilicate minerals?
1D. What is the range of geologic contexts for phyllosilicates on Mars?
1E. What is the relationship between the scale of the orbital detections and
the inter-crystalline or inter-granular details of the rocks and soils?
2. What are the genetic mechanisms by which phyllosilicate minerals
have formed on Mars?
2A. What were the original formation and subsequent alteration pathways?
2B. Can phyllosilicate-bearing rocks be used to infer past environmental
conditions on Mars?
3. What is the relationship between the phyllosilicate minerals
observed in martian meteorites and those detected from orbit?
4. What are the implications of phyllosilicate-bearing rocks for the
development or preservation of pre-biotic chemistry and/or
biosignatures?
Phyllosilicates, Oct. 2008 -8
Investigations needed to address key questions:
Flight Investigations
Workshop on Martian Phyllosilicates
EXTREMELY HIGH PRIORITY
1. Continue operation of the OMEGA and CRISM instruments. Expand
these data sets while the instruments are in place.
2. Continue data reduction of these data sets.
HIGH PRIORITY
3. Acquire ground-truth datasets to confirm spectral interpretations.
A. Part 1—Mars landers
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XRD and IR spectrometer together on a lander to bring the two
datasets together
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Pick a landing site that has diverse, in situ phyllosilicates (hopefully,
both MSL and ExoMars)
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Multiple (cheap) landed missions to explore many environments
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Penetrate into subsurface (~ m) to explore variation with depth—this
is not detectable from orbit
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Spend money to miniaturize instruments so more can be sent
B. Acquire ground-truth datasets: Part 2—Mars Sample Return
Phyllosilicates, Oct. 2008 -9
Investigations needed to address key questions:
Flight Investigations
Workshop on Martian Phyllosilicates
4. Better integration of orbital and landed mission personnel AND datasets
• Increased joint team meetings across instruments
LOWER PRIORITY
5. Additional orbital instruments
• CRISM's follow-up on OMEGA has opened new avenues of research,
and similar possibilities might exist with TIR if technically feasible.
• Increased spatial resolution has the potential to be significant and
might be possible using well-chosen but fewer bands in VNIR
NO PRIORITY ASSIGNED UNTIL AFTER MSL
6. Measure mineralogy more precisely than with CHEMIN
• CheMin will be able to do a good job of distinguishing 1:1 (kaolin and
serpentine groups), 2:1 (smectites, vermiculites, illite, micas, etc.), and
2:1:1 (chlorites) phyllosilicates.
• There are several expected issues with specific identifications due to
the lack of treatments used on Earth (e.g., ethylene glycol saturation).
Phyllosilicates, Oct. 2008 -10
Investigations needed to address key questions:
Terrestrial analogs, experimental, theoretical
Workshop on Martian Phyllosilicates
(Not listed in priority order)
1. Develop a standard set of clay minerals and analog materials (well
characterized by XRD) for comparable studies
• Develop clay mineral standards to circumvent impurity of natural samples.
In some cases it may be possible to synthesize minerals (however there is
difficulty synthesizing many clay minerals at low T). Optimum approach is to
use purified natural materials.
• Create operational definitions of minerals to aid quick identification (a la the
clay community)
2. Expand spectral libraries (add mixtures, textures, grain sizes and solidsolution series)
• Need to improve the spectral libraries, especially of mixtures, textures, and
solid-solution series. Integrate crystallography in mineral identification. Use
XRD to confirm mineral identifications, and include XRD and other additional
data with spectral data in library.
3. Improve our understanding of the detectability of phyllosilicates in
terrestrial analog sites
• Analog studies using same techniques used on Mars
• Sampling depth differences between instruments (esp spectrometers and
XRD).
Phyllosilicates, Oct. 2008 -11
Investigations needed to address key questions:
Terrestrial analogs, experimental, theoretical
Workshop on Martian Phyllosilicates
4. Improve interpretive approaches
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Find ways to detect the role of biology in clay formation
Nonlinear spectral modeling to interpret abundances
Thermodynamic modeling of formation
5. Laboratory simulations of phyllosilicate formation
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Important to understanding impact-induced minerals
Could be a critical direction of research, which is gaining momentum in a
number of institutes, to contribute to understanding out-of-equilibrium
processes that might have played a key role on Mars (and possibly on the
early Earth, too).
Phyllosilicates, Oct. 2008 -12
A Communication Issue
Workshop on Martian Phyllosilicates
What is the best way to deal with variability in confidence and
level of knowledge?
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How can we distinguish non-unique spectral identifications from
definitive mineral identifications? Quantify confidence of match.
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Communicate to community the different levels of confidence for
different phases (if we cannot identify a phase, describe its main
absorptions, e.g., Al-OH vibration)
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Can we set up a quantitative measurement of “robustness”?
Phyllosilicates, Oct. 2008 -13
Appendix: Mineral terms
Workshop on Martian Phyllosilicates
Phyllosilicates
Smectite: general term for a swelling 2:1 phyllosilicate with interlayer cations and H 2O
molecules, includes nontronite, montmorillonite, saponite, and beidellite, among others.
Nontronite: (Na,K,Ca0.5)0.3(Fe+3)2(Si,Al)4O10(OH)2•nH2O, a ferric montmorillonite, Mg and Fe
also possible interlayer cations.
Montmorillonite: (Na,K,Ca0.5)0.3 (Al,Mg)2Si4O10(OH)2•nH2O, Mg and Fe also possible interlayer
cations.
Beidellite: (Na,K,Ca0.5)0.3Al2(Si,Al)4O10(OH)2•nH2O, Mg and Fe also possible interlayer cations.
Sepiolite: Mg4Si6O15(OH)2•6H2O
Muscovite: KAl2(AlSi3)O10(OH)2 , on Earth the most common mica mineral.
Kaolin group: kaolinite, dickite, nacrite, or halloysite, generally Al2Si2O5(OH)4
Serpentine group: lizardite, chrysotile, antigorite, generally Mg3Si2O5(OH)4
Prehnite: Ca2Al2Si3O10(OH)2 On Earth, typically forms as a result of low-grade metamorphism
or hydrothermal alteration.
Non-Phyllosilicates
Pumpellyite: Ca2(Mg,Fe+2)Al2(SiO4)(Si2O7)(OH)2•H2O, An indicator mineral of the prehnitepumpellyite metamorphic facies, typically associated with chlorite, epidote, quartz, calcite
and prehnite.
Epidote: Ca2(Al,Fe+3)3(SiO4)3(OH). Structurally complex mineral found in metamorphic and
hydrothermally altered (a common alteration product of plagioclase) rocks.
Analcime: NaAlSi2O6•H2O.
Phyllosilicates, Oct. 2008 -14