Mineral Species: Sphalerite
Chemical Formula: ZnS
Chemical Name: Zinc Sulfide
Mineral Class: Sulfide
Mineral Notes: Sphalerite is a common sulfide and an important ore of Zinc. It is often called Zincblende or Black Jack. The mineral most commonly occurs in hydrothermal veins in all types of rock, especially with other sulfides, like Galena. Nearly all Sphalerite contains some Iron in solid solution, which affects its appearance and properties. Identification is made on the basis of its perfect cleavage and resinous luster.
Description: The front and sides of this specimen are covered by black, highly lustrous crystals of Sphalerite. Some show marked irridescence. The reverse is made of more massive material. Overall, this is a very attractive specimen of a rare mineral for the Cornish location.