THE MINERAL COPIAPITE

Chemistry: (Fe, Mg)Fe₄(SO₄)₆(OH)₂ - 20H₂O, Hydrated Iron Magnesium Sulfate Hydroxide.
Class: Sulfates
Group: Copiapite
Uses: Only as mineral specimens.
Specimens

Copiapite is a secondary mineral that forms from the oxidation of iron sulfide deposits. At times it has been know to form rather quickly as a crust on exposed iron sulfide ore bodies at mines and sulfide rich coal dumps. It is named for the famed mineral locality at Copiapo, Chile which is where it was first discovered. It is difficult to distinguish copiapite from other similar hydrated iron sulfates without X-ray studies, however its confusion with yellow encrusted uranium minerals can be easily distinguished by its paler color, non-radioactivity and non-fluorescence. Specimens can be rather attractive, but they can lose water and should be stored in a closed container.

Copiapite lends its good name to a group of similar triclinic, hydrated, iron sulfates called the Copiapite Group. Although not a lot of creativity went into their names, the members of this group are all distinct minerals. The general formula of this group is AFe₄(SO₄)₆(OH)₂ - 20H₂O, where A has a positive 2 charge and can be either magnesium, iron, copper, calcium and/or zinc. The formula can also be B_2/3Fe₄(SO₄)₆(OH)₂ - 20H₂O, where B has a positive 3 charge and can be either aluminum or iron.
These are the members of the Copiapite Group:

Aluminocopiapite (Hydrated Aluminum Iron Sulfate Hydroxide)
Calciocopiapite (Hydrated Calcium Iron Sulfate Hydroxide)
Copiapite (Hydrated Iron Magnesium Sulfate Hydroxide)
Cuprocopiapite (Hydrated Copper Iron Sulfate Hydroxide)
Ferricopiapite (Hydrated Iron Sulfate Hydroxide)
Magnesiocopiapite (Hydrated Magnesium Iron Sulfate Hydroxide)
Zincocopiapite (Hydrated Zinc Iron Sulfate Hydroxide)

THE PHYSICAL CHARACTERISTICS OF COPIAPITE:

Color is yellow, orange, sulfur-yellow, golden-yellow, greenish-yellow to ocher.
Luster is pearly to dull.
Transparency: Specimens are translucent to opaque.
Crystal System is triclinic: bar 1.
Crystal Habits include aggregates of small platy or scaly masses, encrustations and granular masses. Individual crystals are rare.
Cleavage is perfect in one direction.
Fracture is uneven.
Hardness is 3.5 - 3.
Specific Gravity is approximately 2.1 (light even for translucent minerals).
Streak is pale yellow.
Other Characteristics: Dissolves in water, is non-flourescent and has a metallic taste.
Associated Minerals include pyrite, other iron sulfides and other secondary minerals.
Notable Occurrences include Copiapo (hence the name), Atacama, Chile; France; Spain; Germany; Utah, California and Nevada, USA.
Best Field Indicators are solubility, density, color, non-flourescence and taste.