Formula: Cu₆(Cu₄C²⁺₂)As₄S₁₂S where C²⁺ = Fe²⁺, Zn, Cu, Hg and/or other species

Species:

Colour: Grey-black, steel-gray, iron-gray, black

Lustre: Metallic

Hardness: 3 – 4½

Crystal System: Isometric

Member of: Tetrahedrite Group; Tennantite Subgroup

Name: Originally called “gray sulphuret of copper in dodecahedral crystals” in 1817 by James Sowerby.
Renamed in 1819 by William Phillips in honor of Smithson Tennant (1761-1815), English chemist of independent means. Tennant established the beneficial nature of using limestone to reduce soil acidity. He and William Hyde Wollaston, who was then his chemical assistant, analyzed graphite and diamond and found that graphite and diamond were both carbon. He analyzed meteorites and found nickel in them, as well as finding iodine in sea water. Tennant’s fame, however, is firmly based on his discovery of the elements iridium and osmium.

First Recorded Locality: Cornwall – England, UK