# Presentation: 273781

## Discussion Summary 

- October 21-23, 2008
- Paris, France
**Discussion Summary**** **
- Compiled by:  Jean-Pierre Bibring, David Beaty, David Bish, Janice Bishop, Jack Mustard, Eldar Noe Dobrea, Sabine Petit, Francois Poulet, Leah Roach

## Consensus Position on Status (Oct. 2008) of Phyllosilicate Mineral Detections on Mars

- 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: well-supported mineral interpretations, and mineral identifications that needed additional information. A partial listing of these categories follows:

_**Generally Accepted by Conference Participants **_

**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**

**Mixed-layer illite/smectite, smectite/chlorite**
**Ca- and Na-zeolite (analcime has been proposed)**
**Prehnite**
**Pumpellyite, epidote**
**Serpentine group**

_**More information needed**_

## Phyllosilicates on Mars: Key Questions (1 of 5)

***. 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 on Mars:  Key Questions (2 of 5)

***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 on Mars:  Key Questions (3 of 5)

***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 m?
- How to scale between km-scale OMEGA and cm-scale lab studies?

## Phyllosilicates on Mars:  Key Questions (4 of 5)

***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***_***?***
- 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?***
- 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?

## 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 pre-biotic 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

- 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 pre-biotic 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 on Mars:**** **** *****Key Questions (5 of 5)***

## Phyllosilicates on Mars:  Summary of Key Questions, Oct. 2008

***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?***
***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?***

## Investigations needed to address key questions:Flight Investigations

- Continue operation of the OMEGA and CRISM instruments.  Expand  these data sets while the instruments are in place.
- Continue data reduction of these data sets.
_*HIGH PRIORITY*_
- Acquire ground-truth datasets to confirm spectral interpretations.
- Part 1—Mars landers
- XRD and IR spectrometer together on a lander to bring the two datasets together
- Pick a landing site that has diverse, *in situ* phyllosilicates (hopefully, both MSL and ExoMars)
- Multiple (cheap) landed missions to explore many environments
- Penetrate into subsurface (~ m) to explore variation with depth—this is not detectable from orbit
- Spend money to miniaturize instruments so more can be sent
- Acquire ground-truth datasets:  Part 2—Mars Sample Return

**Investigations needed to address key questions:****Flight Investigations**

## Investigations needed to address key questions:Flight Investigations

- Increased joint team meetings across instruments
_*LOWER PRIORITY*_
- 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*_
- 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).

**Investigations needed to address key questions:****Flight Investigations**

## Investigations needed to address key questions:Terrestrial analogs, experimental, theoretical

*(Not listed in priority order)*
- 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 solid- solution 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).

## Investigations needed to address key questions:Terrestrial analogs, experimental, theoretical

- 4.  Improve interpretive approaches
- 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
- 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).

## A Communication Issue

- What is the best way to deal with variability in confidence and level of knowledge?
- How can we distinguish non-unique spectral identifications from definitive mineral identifications?  Quantify confidence of match.
- 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)‏
- Can we set up a quantitative measurement of “robustness”?

## Appendix:  Mineral terms

_**Phyllosilicates**_
- Smectite:  general term for a swelling 2:1 phyllosilicate with interlayer cations and H2O 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 prehnite-pumpellyite 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.