Dioptase
- Copper emerald
The mineral Dioptase, often referred to as copper emerald or pebble copper emerald because of its usually deep green color, is a rarely occurring ring silicate mineral from the class of " silicates and Germanates ". It crystallizes in the trigonal crystal system with the composition Cu6 [ Si6O18 ] · 6H2O.
Dioptas developed mainly short to long prismatic crystals, but also granular aggregates in the colors of emerald green to turquoise. On the surfaces of transparent to translucent crystals shows a glass-like shine. Also its Mohs hardness of 5 corresponds to the glass and the reference mineral apatite and therefore can be scratched with a knife.
Special Features
Before the blowpipe Dioptas Although infusible, but becomes black. In hydrochloric acid and ammonia it is soluble, with silica ( precipitated silica ) deposits.
Etymology and history
The term comes from the Greek words dia Dioptas for by or through it and optomai for visual means together so transit or passage of view. So that it refers to the visibility of the inner surfaces of the gap.
First described it in 1797 by René -Just Haiiy ( Hauy ) of the mineral and named. As a type locality applies the deposit of " Altyn -Tyube " ( Altyn- Tube) on the river Altyn -Su in the province of Karaganda in Kazakhstan.
Classification
Already in the now outdated but still in use 8th edition of the mineral classification by Strunz was one of Dioptas the mineral class of " silicates and Germanates " and then to the Department of " ring silicates ( cyclo- silicates) ," where he along with chrysocolla, the independent group VIII / E .21 was formed.
The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the Dioptas also included in the category of " silicates and Germanates " and then in the Department of the " ring silicates ( cyclo- silicates) ." This division, however, is further subdivided by the type of ring formation and the possible presence of other anions, so that the mineral according to its composition in the subdivision - is to find " [ Si6O18 ] 12 six- Simple rings without insular complex anions ", where it acts as only member is the unnamed group 9.CJ.30.
The mainly common in English-speaking classification of minerals according to Dana assigns the Dioptas in the class of " silicates and Germanates " there, however, in the fine already divided the department " ring silicates: Six Rings " field. Here he is the only member of the unnamed group 61.01.03 within the subdivision " ring silicates: Six rings with Si6O18 rings; possible (OH ) and find Al- substitution ".
Education and Locations
Dioptase is formed in the oxidation zone of copper deposits and in crevices of limestone, dolomite or sandstone, where it occurs including in paragenesis with calcite, cerussite, chrysocolla, hemimorphite, malachite, Mimetite and Wulfenite.
As a rather rare mineral formation Dioptas can indeed be abundant in part to different sites, overall it is not very common. So far (as of 2011) are about 150 known localities.
Known due to exceptional Dioptasfunde are in addition to its type locality Altyn -Tyube in Kazakhstan, you still Tsumeb in Namibia and Renéville Department Pool in the Republic of Congo, where well -formed crystals up to 5 cm in size were revealed.
In Germany they found the mineral, among others, in the tin mine of Altenberg in Saxony's Erzgebirge. Another locality, Sasel Grebin at the lake in Schleswig -Holstein, has not been regarded as certain.
Other sites are including in Angola, Argentina, Australia, Chile, France, Iran, Italy, the Democratic Republic of Congo, Morocco, Mexico, Namibia, New Zealand, Peru, the Republic of Congo, Romania, South Africa, Czech Republic and in several states of the USA.
Crystal structure
Dioptas trigonal crystallized in the space group R3 ( Raumgruppen-Nr. 148) with the lattice parameters a = 14.57 Å and c = 7.78 Å and three formula units per unit cell.
Structurally, Dioptase from strongly deformed [ Si6O18 ] - silicate rings, the narrow channels of only 1.77 Å not so easily escape the crystal water contained in contrast to zeolites or can absorb. By carefully heating it can be cast out, however.
Use
Dioptase is mainly as a mineral for collectors of interest. It is only occasionally ground into gemstones because of problematic processing ( relatively low hardness, cleavage, risk of discoloration by heat ). It can be confused with, among others, diopside, fluorite and emerald.