Osumilite
- KFE2 ( Al5Si10 ) O30
Osumilite is a rarely occurring mineral from the mineral group of " silicates and Germanates ". It crystallizes in the hexagonal crystal system with the idealized composition KFE2 ( Al5Si10 ) O30, and is therefore in chemical terms, a potassium iron silicate, which is one structurally to the ring silicates.
Osumilite usually develops transparent to translucent crystals with tabular to prismatic habit of up to five millimeters in size, can also be found in one or raised in massive aggregates. The predominantly dark blue to dark gray, less often green, brown or black, crystals have a glass-like luster.
Special Features
Osumilite is strong dichroically, that shows the passage of light from two different directions, two different colors. Continuous light toward the optical main axis leaves the osumilite light blue to blue-violet, pale pink or pale yellowish brown appear. Perpendicular to it is colorless or brown.
Etymology and history
Osumilite was first found in 1956 on the Sakkabira Ōsumi Peninsula in Japan and described by Akiho Miyashiro, who named the mineral after nOne type locality.
Classification
In the now outdated but still in use 8th edition of the mineral classification by Strunz the osumilite belonged to the general ward of the " ring silicates ( cyclo- silicates) ," where he. Together with Milarite the " Milarite - osumilite group " with the system no VIII/E.22 and the other members Almarudit, Armenit, Berezanskit, Brannockit, Chayesit, Darapiosit, Dusmatovit, Eifelit, Emeleusit, Faizievit, Poudretteit, Merrihueit, Oftedalit, osumilite - (Mg), roedderite, Shibkovit, Sogdianit, Sugilite, Trattnerit, Yagiit and Yakovenchukit - (Y) was formed.
The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the osumilite likewise in the department of " ring silicates ( cyclo- silicates) " a. However, this is further subdivided by the type of ring structure, so that the mineral " 12 [ Si6O18 ] - six double rings " according to its composition in the sub-division is to find where it together with Almarudit, Armenit, Berezanskit, Brannockit, Chayesit, Darapiozit, Dusmatovit, Eifelit, Friedrichbeckeit, Merrihueit, Milarite, Oftedalit, osumilite - (Mg), Poudretteit, roedderite, Shibkovit, Sogdianit, Sugilite, Trattnerit and Yagiit forms the unnamed group 9.CM.05.
The mainly common in English-speaking classification of minerals according to Dana assigns the osumilite in the class of " silicates and Germanates " there, however, in the fine already divided the department " ring silicates: Condensed Rings " field. Here he is in the " Milarite - osumilite group ( Milarite - osumilite subgroup ) " with the system no. 63.02.01a within the subdivision " ring silicates: Condensed, 6 - membered rings " to find.
Education and Locations
Osumilite formed in metamorphic Granulit facies ( MP / HT) at temperatures of about 1000 ° C and pressures in the range of about 8 to 10 kbar. There he found mostly in drusen as deposition from the gas phase and a matrix of rhyolite and dacite.
Apart from its type locality Sakkabira on Ōsumi Osumilitn was found in Japan still at Sakurajima and the Aira caldera in Kyushu.
Globally, could the mineral (as of 2010) are detected in 26 localities: in the Antarctic region Enderbyland; at the discounted cap ( Kemnath, Bavaria ), Blue tip ( Eschwege, Hesse ) and at Ettringer Bellerberg ( Ettringen, Rhineland -Palatinate ) in Germany; Mont Denise at Espaly -Saint -Marcel, in Haute -Loire; on Pauliberg in Austria; at Visakhapatnam in India; Vesuvius and Monte Arci in Italy; in the Canadian province of Labrador; on the North Island in New Zealand; in Norwegian Rogaland county; in Aldanhochland ( Eastern Siberia ) in Russia; Namaqualand in South Africa; in the Tajik part of the Alai Mountains; on the Labwor Hill in Uganda and in Tarpa in the Hungarian Szabolcs- Szatmár- Bereg.
Crystal structure
Osumilite crystallized hexagonal space group P6/mcc ( Raumgruppen-Nr. 192) with the lattice parameters a = 10.09 Å and c = 14.33 Å and two formula units per unit cell.