Stibnite-calcite from Romania. (public display, Carnegie Museum of Natural History, Pittsburgh, Pennsylvania, USA)

A mineral is a naturally-occurring, solid, inorganic, crystalline substance having a fairly definite chemical composition and having fairly definite physical properties. At its simplest, a mineral is a naturally-occurring solid chemical. Currently, there are over 4900 named and described minerals - about 200 of them are common and about 20 of them are very common. Mineral classification is based on anion chemistry. Major categories of minerals are: elements, sulfides, oxides, halides, carbonates, sulfates, phosphates, and silicates.

The sulfide minerals contain one or more sulfide anions (S-2). The sulfides are usually considered together with the arsenide minerals, the sulfarsenide minerals, and the telluride minerals. Many sulfides are economically significant, as they occur commonly in ores. The metals that combine with S-2 are mainly Fe, Cu, Ni, Ag, etc. Most sulfides have a metallic luster, are moderately soft, and are noticeably heavy for their size. These minerals will not form in the presence of free oxygen. Under an oxygen-rich atmosphere, sulfide minerals tend to chemically weather to various oxide and hydroxide minerals.

Stibnite is an antimony sulfide mineral (Sb2S3). Stibnite is quite distinctive for in forming long, slender crystals. It has a metallic luster, a silvery-gray color, is fairly soft (H=2), and has a dark gray streak. Stibnite has economic value - it’s mined in several parts of the world for antimony (Sb). The most significant modern source of stibnite specimens is South China.

Geologic context & age: Inner Carpathian Volcanic Belt, Miocene-Pliocene

Locality: Breiner Mine, Baiut, northern Romania

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