Osumilite is a very rare potassium-sodium-iron-magnesium-aluminium

silicate mineral Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, silica (silicon dioxide, ) is usually consid ...

. Osumilite is part of the milarite group (also known as the milarite-osumilite group) of

cyclosilicate Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, silica (silicon dioxide, ) is usually consid ...

Characteristics

Osumilite chemical formula is .Don S. Goldman, George R. Rossman (1978): ''The site distribution of iron and anomalous biaxiality in osumilite'', In: ''American Mineralogist'', 63, S. 490-498
(PDF, 961 kB)
E. Olsen, T. E. Bunch (1970): ''Compositions Of Natural Osumilites'', In: ''The American Mineralogiste'', 55, S. 875 - 879
(PDF, 328 kB)
It is translucent and the typical coloring is either blue, black, brown, or gray. It displays no cleavage and has a

vitreous Vitreous may refer to: Materials * Glass, an amorphous solid material ** Vitreous enamel, a material made by fusing powdered glass to a substrate by firing * Vitreous lustre, a glassy luster or sheen on a mineral surface Biology * Vitreous bod ...

luster. Osumilite has a hardness between 5-6 on the

Mohs hardness scale The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by th ...

. The

hexagonal In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°. Regular hexagon A '' regular hexagon'' has ...

crystal structure In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric pattern ...

of osumilite is an unusual molecular make-up. The primary unit is a double ring, with a formula of . Normal cyclosilicate have rings composed of six silicate

tetrahedron In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all ...

s; . In a double ring structure, two normal rings are linked by sharing six oxygens, one from each tetrahedron in each six membered ring.http://www.galleries.com/minerals/silicate/osumilit/osumilit.htm ''Mineral Galleries''

Occurrence

Osumilite, was first discovered as grains in

volcanic rocks Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcan ...

near Osumi,

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...

. It was confused with a similar mineral

cordierite Cordierite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: to . A high-temperat ...

because of their similar coloring. It can be found in high-grade

metamorphic rocks Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, caus ...

xenoliths A xenolith ("foreign rock") is a rock fragment (country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term ''xenolith'' is almost exclusively used to describe inclusions in ign ...

and in the

groundmass The matrix or groundmass of a rock is the finer-grained mass of material in which larger grains, crystals, or clasts are embedded. The matrix of an igneous rock consists of finer-grained, often microscopic, crystals in which larger crystals, ...

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals ( phenocrysts) in an otherwise fine-grained groundmass. The miner ...

and

dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained ( aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyo ...

.http://www.handbookofmineralogy.org/pdfs/osumilite.pdf ''Handbook of Mineralogy'' Osumilite is found in the

Obsidian Cliffs Obsidian () is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock. Obsidian is produced from felsic lava, rich in the lighter elements such as silicon, ...

Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...

;

Sardinia Sardinia ( ; it, Sardegna, label=Italian, Corsican and Tabarchino ; sc, Sardigna , sdc, Sardhigna; french: Sardaigne; sdn, Saldigna; ca, Sardenya, label= Algherese and Catalan) is the second-largest island in the Mediterranean Sea, aft ...

Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...

; Kagoshima and Yamanashi Prefecture, Japan; and the

Eifel The Eifel (; lb, Äifel, ) is a low mountain range in western Germany and eastern Belgium. It occupies parts of southwestern North Rhine-Westphalia, northwestern Rhineland-Palatinate and the southern area of the German-speaking Community of ...

district in

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwee ...

. Osumilite pseudomorphs are known from a number of ultrahigh-temperature rocks, including those of southern Madagascar.

References

{{reflist Magnesium minerals Iron minerals Potassium minerals Aluminium minerals Cyclosilicates Hexagonal minerals Minerals in space group 192

Characteristics

Occurrence

See also

References