PHYSICAL PROPERTIES:
Chemistry: Co3(AsO4)2-8(H2O)
Composition: Hydrated Cobalt Arsenate
Class: Phosphates
Group: Vivianite
Crystal system: monoclinic
Fracture: not significant
Hardness: 1.5-2.5
Specific gravity: 2.9
Luster: glassy to pearly
Streak: pale red
Cleavage: perfect in one direction
Color: Bluish pink to deep raspberry red
Transparency: transparent to translucent
Associated Minerals: silver, cobaltite,
skutterudite, and other cobalt vein minerals.
COMPOSITION:
Hydrous cobalt arsenate (37.5% CoO, 38.4% As205,
24.1% H20, (can have some nickel in place of
the cobalt)
DISTINGUISHING CHARACTERISTICS:
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.
ENVIRONMENT:
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.
CRYSTAL DESCRIPTION:
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.
TESTS:
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.
LOCALITIES:
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.
USES:
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".
Top
Click here to
see our Specimens
