Seventh International Conference on Mars 3004.pdf

Mars surface mineralogy: Implications of kieserite group crystal chemistry (Mg, Fe2+, Mn2+, Zn, Ni, Co) SO4·H2O. J.J. Papike, P.V. Burger, J.M. Karner, C.K. Shearer, Astromaterials Institute, University of New Mexico, Albuquerque, New Mexico 87131. [email protected].

INTRODUCTION. Previous missions to Mars have kieserite may reflect the Co/Ni of the impactor if, in- shown that the element sulfur and the sulfate minerals deed, impact played an important role in its formation are important constituents of the martian regolith and or redistribution. bedrock. Both sulfates and sheet silicates, including CRYSTAL CHEMISTRY. This discussion of kie- several clay minerals, have been identified by spectral serite crystal chemistry is derived from Hawthorne et techniques such as OMEGA and CRISM (Bibring et al. (2000)[10] and Hawthorne et al. (1987)[11]. Figure al. 2006)[1]. The mid-infrared emission spectroscopy 2a-c displays the structure in three projections, down of sulfates is reviewed by Lane (2007)[2] and the Ra- the c-axis, down the b-axis, and down the a-axis. The man spectral characteristics of the magnesium sulfate kieserite structure is a type of framework structure hydrates are reviewed by Wang et al. (2006)[3]. The where chains of corner-sharing octahedra (blue) are experimental stability of magnesium sulfate hydrates is cross linked by sulfate tetrahedra (yellow). Figure 2a, reviewed by Chipera and Vaniman (2007)[4]. Figure projection down c, shows the C-centered face for 1 illustrates a simplified phase diagram from [4] and space group C2/c. The corners of the unit cell and the summarizes the different crystal structure types. The center of the C-face of the unit cell have identical focus of this paper is on the magnesium sulfate hy- symmetry environments. The oxygen (1) and oxygen drate, kieserite, because it has been positively identi- (2) ligands connect octahedra and tetrahedra. The im- fied as an important sulfate mineral on Mars. The sul- portant oxygen (3) ligand bridges between two octahe- fate polyhydrates of magnesium have OH related ab- dra and forms two strong hydrogen bonds (hydrogen sorptions in the NIR but they are less distinct from in red). These are the bonds that give rise to the dis- each other than kieserite, possibly due to their weaker tinctive spectral signature of kieserite. Figure 2b hydrogen bonding. Kieserite has a 2.4 micron band shows the structure projected down b. Both the sulfate that is shifted toward longer wavelengths presumably tetrahedra and O3 oxygen sit on two-fold axes that run because of its stronger hydrogen bonding (Greg parallel to b. In this projection the H-O-H bond link- Swayze 2007, personal communication). As such, age appears collinear but it is not (note Fig. 2a and 2c). kieserite has a high spectral contrast compared to other This projection also illustrates the corner-sharing con- polyhydrates so it is more easily detected based on the tinuous chains of octahedral. Figure 2b gives the false unique wavelength position of the 2.4 micron band and impression that the octahedral chains are extended but its relatively greater intensity. Also, recent studies by 2c shows that the chains are really quite kinked. Pure Chipera and Vaniman [4] show that kieserite, once kieserite contains Mg in the octahedral site. However, crystallized, is more resilient that the other Mg sulfate we do not know if martian kieserite is a pure Mg end- hydrates so it can remain metastable for long periods member or is a solid solution with other kieserite of time in the dry, cold, martian regolith. Kieserite group species (note Table 1). Figure 3 (after Wildner resists dessication at equatorial Mars conditions, but and Giester (1991) [12] shows the variation of unit-cell can slowly hydrate to form more hydrous species at parameters with composition, arranged so that the higher latitudes. ionic radii of the octahedral cation increases to the right. It is apparent that ionic radii are a significant Papike et al. (2006a[5], 2006b[6], and 2007[7]) review influence on the a-axis, c-axis, and volume but not the the potential of sulfate jarosite for recording atmos- b-axis. This means that most of the expansion caused pheric-fluid-rock interactions on the surface of Mars. by larger cation substitution takes place along a and c This study (in progress) is attempting to do the same but not b. This can be explained by pathways across thing for kieserite. As an example of the potential of the unit cell in the axial directions and counting the kieserite as a recorder of martian processes we will number of octahedra that are traversed (at the same refer to meteorite impact as an important process in the level). Traverses along a and c encounter two octahe- formation and redistribution of sulfates on Mars, (see dra but a traverse along b (note Figure 2a) traverses Burt et al. 2006 [8] and McLennan et al. 2006 [9]. Co- only one octahedron. Therefore the chemical expan- balt and nickel form end-member kieserite group min- sion causes by increased ionic radii affects b less than erals, cobaltkieserite and dwornikite (see Table 1). a or c. Table 2 describes additional structural details. Therefore once we recover kieserite from Mars, either It shows the site symmetry for each cation and the as a martian sulfate in a martian meteorite or from a multiplicity of each atom (the number of atoms per future martian surface sample return, the Co/Ni ratio in unit cell). The Mg cation sits on an inversion center Seventh International Conference on Mars 3004.pdf

and sulfur and O3 on two fold axes. These are special positions with multiplicity 4. Oxygen 1 and 2 and Figure 2a. hydrogen are in general positions (no special symme- try restrictions) and have the maximum multiplicity, which is 8. Thus there are 4 Mg, 4 S, 20 O, and 8 H

atoms per unit cell. Table 3 shows selected bond

lengths. The tetrahedra have two symmetrically iden- tical S-O(1) and two symmetrically identical S-O(2) bond lengths. The Mg-containing octahedra have 3 pair of symmetrically identical bonds, Mg-O(1), Mg- O(2), and Mg-O(3). Note that the Mg-O(3) bond is the longest probably because of the hydrogen bonding O3

to O(3). Two strong (short) hydrogen bonds are H- O2 O1 O(3) and two weak (long) bonds are H-O(2)). ACKNOWLEDGEMENTS. This research was

funded by a NASA/ Cosmochemistry grant to JJP. REFERENCES. [1] Bibring et al.(2006) Nature, 312, 400-404. [2] Lane (2007) Am. Min., 92, 1-18. [3] Wang et al. (2006) GCA, 70, 6118-6135. [4] Chipera and Vaniman (2007) GCA, 71, 241-250. [5] Papike et al. (2006a) GCA, 70, 1309-1321. [6] Papike et al. Figure 2b. (2006b) Am. Min., 91, 1197-1200. [7] Papike et al. (2007) Am. Min., 92, 444-447. [8] Burt et al. (2006) LPI Mars Sulfate Workshop, 7004.pdf. [9] McLennan et al. (2006) LPI Mars Sulfate Workshop, 7045.pdf. [10] Hawthorne et al. (2000) RiMG, 40, 1-112. [11]

Hawthorne et al. (1987) Neues Jahrbuch Min. Abh., O1 O2 157, 121-132. [12] Wildner and Giester (1991) N. Jb. O3 Min. Mh. H 7, 296-306.

Figure 1.

Anhydrous 100 Kieserite (1) 75 (6) 4) ite ( r

) e d 50 eyit hy C rk xa ° ta e ( S H Figure 2c.

25 ) e te(5 r ri hyd Epsomite (7) u nta t 0 day Pe a

r

e

p -25 M ars m s urfac e e at V T -50 ikin g Lan der 1 site night -75 (sum mer)

-100 O3 0 20 40 60 80 100 Relative Humidity O1 O2

Selected Mg-sulfate hydrates: structural types Hexahydrite MgSO ·6H O I 4 2 Isolated T and O Epsomite MgSO4·7H2O II Starkeyite MgSO4·4H2O Finite clusters of T and O

III Pentahydrite MgSO4·5H2O Chains of T and O

IV Kieserite MgSO4·1H2O Framework, T-O-T-O Seventh International Conference on Mars 3004.pdf

Figure 3. Table 2. Crystal structure aspects of kieserite: Z, number of formula units per unit cell = 4. 390

V Atom Wyckoff Site Site Symmetry Multiplicity 380 Notation

Mg b 1 4

370 S e 2 4 O (1) f 1 8 O (2) f 1 8 360 O (3) e 2 4

H f 1 8 350 Atoms per unit cell: 4 Mg; 4 S; 20 O2-; 8 H

340

Table 3. Selected interatomic distances for kieserite (Haw- 8.0 c thorne et al. 1987).

7.8 Kieserite S-O (1) 1.466 Å x 2

S-O (2) 1.478 Å x 2 7.6 b Mg-O (1) 2.019 Å x 2 Mg-O (2) 2.041 Å x 2 7.4 Mg-O (3) 2.172 Å x 2 Longer because of H bonding H-O (3) 0.86 Å x 2 Strong bond 7.2 a H-O (2) 1.92 Å x 1 Weak bond

7.0

6.8 Ni Mg ZnCo Fe Mn 6.6 .68 .70 .72 .74 .76 .78 .80 .82 .84

Table 1. Kieserite group minerals.

Beta Name Formula a (Å) b (Å) c (Å) angle S.G. (degrees)

Dwornikite NiSO4·1H2O 6.824 7.594 7.457 117.8 C2/c

Kieserite MgSO4·1H2O 6.891 7.624 7.645 117.7 C2/c

Gunningite ZnSO ·1H O 6.925 7.591 7.635 118.2 C2/c 4 2

Cobaltkieserite CoSO4·1H2O 6.98 7.588 7.639 118.6 C2/C

Szomolnokite FeSO4·1H2O 7.078 7.549 7.773 118.7 C2/c

Szmikite MnSO4·1H2O 7.116 7.667 7.92 118.1 C2/c