Allactite
(repeating unit)Mn7(AsO4)2(OH)8 IMA symbol Ala[1] Strunz classification 8.BE.30 Dana classification 41.2.1.1 Crystal system Monoclinic Crystal class Prismatic (2/m)
(same H-M symbol) Space group P21/a Unit cell a = 11.03, b = 12.12
c = 5.51 [Å], β = 114°, Z = 2 Identification Color Brown, dark to light purplish red, brownish red, colorless to white Crystal habit Elongated prisms, bladed, tabular, rosette-like aggregates Cleavage Distinct, {001} Fracture Uneven Tenacity Brittle Mohs scale hardness 4.5 Luster Vitreous, slightly greasy on fracture surfaces Streak Gray to faint brown Specific gravity 3.83 (meas.), 3.94 (calc.) Optical properties Biaxial (−) Refractive index nα = 1.755–1.761
nβ = 1.772–1.786
nγ = 1.774–1.787 Pleochroism X = blood-red; Y = pale yellow; Z = sea-green 2V angle ~0° References [2][3][4]
(same H-M symbol)
c = 5.51 [Å], β = 114°, Z = 2
nβ = 1.772–1.786
nγ = 1.774–1.787
Allactite is a rare arsenate mineral of metamorphosed manganese zinc ore deposits. It is found in Sweden and New Jersey, US. Its name originated from Greek αλλάκτειν (allaktein) meaning "to change", referring to the strong pleochroism of the mineral.[3]
References
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ Allactite. Mindat
- ^ a b Allactite. Handbook of Mineralogy
- ^ Moore P. (1968). "Crystal chemistry of the basic manganese arsenate minerals: II. The crystal structure of allactite" (PDF). American Mineralogist. 53: 733–741.
Bibliography
- Palache, P.; Berman H.; Frondel, C. (1960). "Dana's System of Mineralogy, Volume II: Halides, Nitrates, Borates, Carbonates, Sulfates, Phosphates, Arsenates, Tungstates, Molybdates, Etc. (Seventh Edition)" John Wiley and Sons, Inc., New York, pp. 785-787.
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