Bulgarian Sphalerite
Sphalerite is zinc sulfide (ZnS) and the main ore of zinc, the metal used to galvanise steel against rust. Its name comes from the Greek word for treacherous: miners often mistook it for galena, but it gave no lead. German miners called it blende, from a word meaning to deceive, and zinc blende is still a common name for it. Its colour depends on how much iron it holds, from black and almost metallic to yellow, red and green, and its lustre ranges from resinous to almost diamond-like.
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Mineral guide
Bulgarian Sphalerite
Bulgarian sphalerite
The sphalerite in this collection comes from Bulgaria. Sphalerite and galena are the two main ore minerals of the lead-zinc deposits in the Rhodope Mountains, in the south of the country. Bulgarian sphalerite ranges from lustrous black, iron-rich crystals to cleiophane, the nearly iron-free variety, which is pale green to yellow and often translucent. The dispersion of sphalerite, the way it splits light into colours, is more than three times that of diamond, so clear cleiophane crystals can flash with spectral colours.
Other minerals in these specimens
Most of these specimens are mixed: sphalerite usually sits on white quartz and grows together with galena, and some pieces also carry pyrite, chalcopyrite or calcite. The title of each listing names every mineral in the piece, and mixed specimens also appear in the collection of each mineral they contain.
How to recognise sphalerite
Sphalerite has a Mohs hardness of 3.5 to 4, so a knife scratches it. A useful test is the streak: even black sphalerite leaves a pale yellow to brown powder on unglazed porcelain, while the streak of galena is grey. It has perfect cleavage in six directions, so it splits easily along flat, shiny planes.
Caring for sphalerite
Because of its many cleavage directions, sphalerite is brittle and can chip if knocked. Dust it with a soft dry brush, avoid ultrasonic cleaners and sudden temperature changes, and store specimens so they do not touch each other.
Each listing shows the weight and photos of the actual specimen.