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.
Did you know?
In 1863 Ferdinand Reich and Theodor Richter of Freiberg were testing zinc ore for thallium when a bright indigo line appeared in its spectrum. It belonged to a new element, named indium after the color. Reich was colorblind, so Richter had to do the looking.
Today indium is used in the coating of touchscreens.
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.
The title of each listing names every mineral in the piece. Each listing shows the weight and photos of the actual specimen.