Crystal Copper

Chemical Formula

Cu

Composition

Copper, commonly associated with iron and silver

Variable Formula

(Cu,Fe,Ag)

Color

Copper-red to brown. Tarnishes green, sometimes also blue, brown, red, or black.

Streak

Copper-red. Streak shiny.

Hardness

2.5 - 3

Crystal System

Isometric

Crystal Forms 
and Aggregates

Often found as distorted masses or extremely distorted crystals. Crystals, which are uncommon, are usually cubic or dodecahedral with modified faces. Octahedral crystals do occur, but are very rare. Also occurs as flattened crystals, scales, dendrites, and wires.

Transparency

Opaque

Specific Gravity

8.93

Luster

Metallic

Cleavage

None

Fracture

Hackly

Tenacity

Ductile and Malleable

Other ID Marks

1) Tarnish. Green tarnish speckled throughout a specimen, may also be blue, red, or black.

2) Excellent conductor of electricity. Copper is the second best conductor of electricity (after Silver).

In Group

Native Elements; Metallic Elements

Striking Features

Unique color and crystal habits; green, blue, and black tarnish; and great malleability and ductility.

Environment

Most common in volcanic basalt rocks, often near the level of contact with sedimentary rock layer. Also in hydrothermal replacement deposits and the oxidation zone of sulfide deposits.

Rock Type

Igneous, Sedimentary, Metamorphic

Popularity (1-4)

1

Prevalence (1-3)

2

Demand (1-3)

1