Sphalerite is a zinc ore mineral that typically contains iron. When it has a high iron content, sphalerite is an opaque black. Gem-quality material has a low iron content, resulting in transparent crystals. Due to its lack of hardness, it is mainly a collector's gemstone. One of the most notable characteristics of sphalerite is its high dispersion (0.156). In fact, the dispersion of sphalerite is over three times that of diamond, which has a dispersion of 0.044. This means that sphalerite has remarkable "fire"; the separation of visible light into colors by refraction or diffraction. In simple terms, this refers to the flashes of color seen when sphalerite is turned in the light.

Due to its composition, sphalerite is also known as "zinc blende". The name "sphalerite" comes from the Greek word, "sphaleros", which means "deceptive". This is because sphalerite is easily mistaken for galena, which is the mineral form of lead sulphide. Gem quality transparent sphalerite is rare. Sphalerite is typically yellow, orange or red. A black, iron rich variety of sphalerite is called marmatite.