Covellite

Formula:  CuS

Origin of name:  For N. Covelli, Italian mineralogist

Crystal system:  Hexagonal

Crystal class:  6/m 2/m 2/m

Twinning:

Unit cell: a = 3.792 Å, c = 16.34 Å

Colour:  Light to dark indigo-blue

Diaphaneity: 

Luster:  Submetallic to dull

Habit:  Crystals thin tabular hexagonal plates; massive, foliated

Hardness:  1.5 to 2

Specific gravity:  4.681

Cleavage:  1; {0001} perfect

Tenacity:  Uneven; brittle, thin laminates

Streak:  Shining gray-black

Synonyms/varieties:

Comments: Most commonly found as secondary mineral in the oxidation zone in sulphide copper deposits. Rarely of primary hydrothermal origin. Widespread in most copper deposits, common as an iridescent tarnish on other sulphides.