- Osumilite
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Osumilite 
Osumilite tablets with mullite from Ochtendung, Eifel, Germany.General Category Cyclosilicate Chemical formula (K,Na)(Fe,Mg)2(Al,Fe)3(Si,Al)12O30·H2O Strunz classification 09.CM.05 Dana classification 63.02.01a.06 Crystal symmetry Hexagonal 6/m 2/m 2/m Unit cell a = 10.15 Å, c = 14.25 Å; Z = 2 Identification Color Black, dark blue, dark brown, pink, gray Crystal habit Crystals tabular to prismatic also anhedral and massive Crystal system Hexagonal; 6/m 2/m 2/m. Twinning Rarely Cleavage None Fracture Subconchoidal Mohs scale hardness 5 - 6 Luster Vitreous Streak Blue-gray Specific gravity 2.62 - 2.64 Optical properties Uniaxial (+) anomalously biaxial Refractive index w=1.545-1.547, e=1.549-1.551 Birefringence 0.004 Pleochroism Strong References [1][2][3] Osumilite a very rare hydrate potassium-sodium-iron-magnesium-aluminium silicate mineral. Osumilite is part of the milarite group (also known as the milarite-osumilite group) of cyclosilicates.
Contents
Characteristics
Osumilite chemical formula is (K,Na)(Fe,Mg)2(Al,Fe)3(Si,Al)12O30·H2O. It is translucent and the typical coloring is either blue, black, brown, or gray. It displays no cleavage and has a vitreous luster. Osumilite has a hardness between 5-6 on the Mohs hardness scale.[3]
The hexagonal crystal structure of osumilite is an unusual molecular make-up. The primary unit is a double ring, with a formula of Si12O30. Normal cyclosilicate have rings composed of six silicate tetrahedrons; Si6O18. In a double ring structure, two normal rings are linked by sharing six oxygens, one from each tetrahedron in each six membered ring.[4]
Occurrence
Osumilite, was first discovered as grains in volcanic rocks near Osumi, Japan. It was confused with a similar mineral cordierite because of their similar coloring. It can be found in high-grade metamorphic rocks, xenoliths and in the groundmass of rhyolite and dacite.[2]
Osumilite is found in the Obsidian Cliffs, Oregon; Sardinia, Italy; Kagoshima and Yamanashi Prefecture, Japan; and the Eifel district in Germany.[2]
See also
References
- ^ Mindat.org
- ^ a b c http://www.handbookofmineralogy.org/pdfs/osumilite.pdf Handbook of Mineralogy
- ^ a b Webmineral.com
- ^ http://www.galleries.com/minerals/silicate/osumilit/osumilit.htm Mineral Galleries
Categories:- Magnesium minerals
- Iron minerals
- Potassium minerals
- Aluminium minerals
- Cyclosilicates
- Hexagonal minerals
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