THE MINERAL BROCHANTITE
- Chemistry: Cu4SO4(OH)6, Copper Sulfate Hydroxide.
- Class: Sulfates
- Uses: A minor ore of copper and as mineral specimens.
Brochantite is a popular mineral for collectors and in some places it has been an important ore of copper. It typically forms acicular or fibrous crystals aggregated into 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.
Brochantite is similar to other fibrous green copper minerals that form in oxidation zones such as the carbonate mineral malachite, the halide mineral atacamite and the closely related sulfate mineral antlerite. This brings up a number of identification problems. Acicular malachite will effervesce in warm hydrochloric acid and brochantite will not. Atacamite is slightly softer and is usually less transparent. Antlerite is all but indistinguishable by ordinary means although its terminations are typically flatter than the rounded terminations of brochantite.
- Color is a bright emerald green or dark green to almost black.
- Luster is vitreous to pearly on cleavage surfaces.
- Transparency: Crystals are transparent to translucent.
- Crystal System is monoclinic; 2/m.
- Crystal Habits include acicular or fibrous crystals aggregated into coatings and tufts as well as small tabular crystals and reniform, massive or granular specimens. Terminations tend to be rounded or dome-like. Twinning is common and gives an orthorhombic look to larger crystals.
- Cleavage is perfect in one direction nearly perpendicular to length.
- Fracture is uneven.
- Hardness is 3.5 – 4
- Specific Gravity is approximately 3.9+ (above average for translucent minerals)
- Streak is green.
- Other Characteristics: Does not effervesce in hydrochloric acid.
- Associated Minerals are limonite, cuprite, chrysocolla, cyanotrichite, malachite, langite, posnjakite and azurite.
- Notable Occurrences include numerous locations in Chile; Ural Mountains, Russia; England; Italy; Romania; Zaire and several locations in Arizona, Nevada, California, New Mexico and Utah, USA.
- Best Field Indicators are crystal habit, associations, hardness, cleavage, non-reaction to hydrochloric acid and color.