The Mineral Erythrite
Composition: Hydrated Cobalt Arsenate
Crystal System: monoclinic
Fracture: not significant
Specific Gravity: 2.9
Luster: glassy to pearly
Streak: pale red
Color: Bluish pink to deep raspberry red
Cleavage: perfect in one direction
Transparency: transparent to translucent
Associated Minerals: silver, cobaltite, skutterudite, and other cobalt vein minerals.
Hydrous cobalt arsenate (37.5% CoO, 38.4% As205, 24.1% H20, (can have some nickel in place of the cobalt)
The vivid pink and purple colors of this mineral are electrifying making it nearly unmistakable. There is almost no mineral resembling this except a rare cobalt carbonate (sphaerocobaltite, which effervesces in acid) and a rare related arsenate (roselite). Kaemmererite, a violet-red chlorite, is very similar but does not produce the cobalt bead when heated.
Secondary, weathered, portions of cobalt ore deposits containing minerals such as cobaltite. Erythrite and Annabergite are both important markers of cobalt and nickel ores. They are known by miners as "Cobalt Bloom" and "Nickel Bloom". Annabergite is bright green and is isostructural with erythrite. "Isostructural" means that the two minerals have the same structure but different chemistries.
Crystals are rare. Erythrite usually forms pink earthy crusts and masses. It sometimes forms in slender prisms, and rarely forms radiating accicular crystal clusters. It may also form long flat needles or flattened striated blades.
Fuses into flattened gray mass with arsenical smell. Borax added to a fragment of this mass turns deep blue. Do not put on platinum wire, because of the arsenic.
Most erythrite is found in the form of crusts, but good Erythrite specimens have been found in North America, in Idaho and Ontario Canada. Morocco,Germany and Sornora, Mexico all have fine samples of Erythrite. Many years ago fine crystals with radiating blades found in quartz cavities came from Schneeberg, Saxony. Solid crusts of slender needles have come from Queensland, Australia. Good specimens are not at all common in the United States, although some other US. locations are Nevada, Arizona, New Mexico, and California. Today Bou Azzer, Morocco seems to be the main source for specimens.
Mineral specimens also a very minor ore of cobalt. Its characteristic bright red-purple color is very noticable and was used to spot veins of cobalt-bearing ore.
FACTS & HISTORY:
The Greek word erythros translates "red".
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