Alacránite
Alacranite | ||
---|---|---|
Specific gravity 3.4 - 3.46 | | |
Optical properties | Biaxial (+) | |
Refractive index | nα = 2.390(1) nγ = 2.520(2) | |
Birefringence | 0.1300 | |
References | [2][3][4] |
Alacránite (As8S9) is an
grains up to 0.5 mm across.Composition
When alacranite was first discovered in 1970 by Clark, it was associated with
Structure
X-ray crystallography
The structure of alacranite remained unsolved until further studies collected specimens containing crystals of alacranite. A group that studies seafloor
Fourier analysis
Further studies of a single crystal of alacranite with dimensions 30 × 60 × 120 mm was examined using direct methods, Fourier syntheses and structure refinement resulting in intensities violating the C lattice type and symmetries like h0l reflections with l = 2n + 1 were absent. These results confirm the P2/c space group of alacranite resulting in a structure of two different kinds of cage-like molecules that are packing closely and found in the β-phase.[7] The first molecule is identical to the As4S4 which is realgar where every As atom links one As and two S atoms and that is determined in the structure of the β-phase and realgar. The second molecule in the structure of alacranite is found to be chemically and structurally identical to As4S5 which is uzonite. Upon exposure to light, As4S4 molecule expands its unit cell volume and hence, transfers to As4S5. This transformation could be described to the variation of the inter molecular distances.[7] These coherent orders of both molecules along [110] attributes to the change of the translation symmetry from C (β-phase) to P which is alacranite.[7] In both molecules, the distances of the As-S bond are about 2.205 to 2.238 angstrom. However, the As-As bond distance in the As4S4 is longer than the As-As bond contained in As4S5 molecule within alacranite structure.[8] It was also shown that the unit-cell volume increases proportionally with increasing S content of minerals with ranging composition from As4S4 to As8S9 where alacranite has the biggest unit-cell in this range.[7] Evidence supports that alacranite has a P2/c space group whereas the high-temperature and less content of S form is considered to be a new mineral that corresponds to the species from alacran previously described by which is As4S4 that crystallizes with the space group C2/c and has a smaller volume.[7]
Physical properties
Alacranite occurs as cement in sandy gravel and in
Geologic occurrence
Alacranite was first found in the
Alacranite occurs in the condensation zone of a hydrothermal Hg-Sb-As system in the Uzon caldera. Alacranite could also be found in hydrothermal As-S veins.
It was named alacranite after its occurrence in the Alacran mine in
References
- S2CID 235729616.
- ^ a b c Anthony, J. W; Bi deaux, R.; Bladh, K. & Nichols, M. (2003). "Alacranite AsS. Handbook of Mineralogy. Mineral date publishing" (PDF).
- ^ "Mindat.org".
- ^ "Webmineral data".
- ^ a b [1] Burns, P. and Pervival, J. (2001) Alacranite, As4S4: A new occurrence, new formula and determination of the crystal structure. Canadian Mineralogist, 39, 809-818.
- ^ a b c d Bonazzi P., Bindi L., Popova V., Pratesi G. and Menchetti S. 2003: Alacranite, As8S9: structural study of the holotype and re-assignment of the original chemical formula. American Mineralogist, 88(11-12), pp. 1796-1800/>
- ^ a b c d e [2] Bonnazzi, P. (2006) Light-induced changes in molecular arsenic sulfides: State of the art and new evidence by single-crystal X-ray diffraction. American Mineralogist, 91,1323.
- ^ [3][permanent dead link] Bonnazzi, P. and Bindi, L. (2008) A crystallographic review of arsenic sulfides: effects of chemical variations and changes induced by exposure to light. Mineralogical Crystallography. 223, 132-147.
- ^ [4] Hawthorne, F., Burke, E., Ercit, T., Grew, E., Grice, J., Jambor, J., Puziewicz, J., Roberts, A., and Vanko, D. (1988) New Mineral Names. American Mineralogist. 73, 189.
- ^ "Geologic Setting of the Uzon Caldera, Kamchatka, Far East Russia". Archived from the original on 2008-06-03. Retrieved 2009-12-02.
- Handbook of Mineralogy and references therein (original description by Popova et al. 1986)
- Mindat
- Bonazzi P., Bindi L., Popova V., Pratesi G. and Menchetti S. 2003: Alacranite, As8S9: structural study of the holotype and reassignment of the original chemical formula. American Mineralogist, 88(11-12), pp. 1796–1800; [5]
- Athens, G., Gennadii A. Geologic setting of the uzon caldera, Kamchatka, far east Russia. [6].
- Jambor, J. and Roberts, A (2004) New Minerals Names. American Mineralogist. 89, 249-253.
- Sorrel, C. and Sandstrom, G. (1973) Rocks and Minerals: A Guide to Field Identification. Golden Field Guides. 82-111.