THE MINERAL ANTLERITE

Chemistry: Cu3SO4(OH)4, Copper Sulfate Hydroxide.
Class: Sulfates
Uses: A minor ore of copper and as mineral specimens.
Specimens

Antlerite has been an important ore of copper and forms nice mineral specimens. It typically forms tabular to acicular or fibrous crystals. The acicular crystals often form aggregates of randomly organized coatings and tufts. Its green color is usually a deep and attractive shade. It is formed from the oxidation of copper ore minerals along with other oxidation zone minerals. Once thought to be a rare mineral, antlerite was discovered to be the chief ore at the Chuquicamata copper mines in Chile. Since then its presence has been confirmed at several other copper mines around the world.

Antlerite is similar to other green copper minerals that form in oxidation zones such as the carbonate mineral malachite, the halide mineral atacamite and the closely related sulfate mineral brochantite. This brings up a number of identification problems. Acicular malachite will effervesce in warm hydrochloric acid and antlerite will not. Atacamite is slightly softer and is usually less transparent. Brochantite is all but indistinguishable by ordinary means although its terminations are typically more rounded than the terminations of antlerite.

PHYSICAL CHARACTERISTICS:

Color is a bright emerald green or dark green to almost black.
Luster is vitreous.
Transparency: Crystals are transparent to translucent.
Crystal System is orthorhombic; 2/m 2/m 2/m
Crystal Habits include small tabular crystals and acicular or fibrous crystal aggregates that form into coatings and tufts. Also found in veins and as reniform, massive or granular specimens.
Cleavage is perfect in one direction and poor in another.
Fracture is uneven.
Hardness is 3.5
Specific Gravity is approximately 3.9 (above average for translucent minerals)
Streak is pale green.
Other Characteristics: Does not effervesce in hydrochloric acid and crystals can be vertically striated.
Associated Minerals are limonite, brochantite, cuprite, malachite, gypsum, chalcanthite, atacamite and azurite.
Notable Occurrences include Chuquicamata, Chile; Mexico and the Antler mine (from where it gets its name) and Bisbee, Arizona, Nevada, California, New Mexico and Utah, USA.
Best Field Indicators are crystal habit, associations, hardness, cleavage, non-reaction to hydrochloric acid and color.