Erythrite
Current inventory:  0 gems
 

  
Erythrite is named from the Greek for red, its characteristic deep crimson color.

Discovered in 1832;   IMA status:  Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

Co₃(AsO₄)₂ • 8(H₂O)

Hydrated Cobalt Arsenate

Molecular Weight:

598.76 gm

Composition:

Cobalt

29.53 %

Co

41.55 %

Co₂O₃

Arsenic

25.03 %

As

38.39 %

As₂O₅

Hydrogen

2.69 %

H

24.07 %

H₂O

Oxygen

42.75 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Phophates

Strunz 8th Ed. ID:

7/C.13-70

Nickel-Strunz 10th Ed. ID:

8.CE.40

8 : PHOSPHATES, ARSENATES, VANADATES
C : Phosphates without additional anions, with H₂O
E : With only medium-sized cations, RO₄:H₂O about 1:2.5

Related to:

Vivianite Group. Annabergite-Erythrite Series. Hörnesite-Erythrite Series. The cobalt analogue of Annabergite and Köttigite.

Members of Group:

Vivianite Group: Annabergite, Arupite, Baricite, Erythrite, Hörnesite, Köttigite, Manganohörnesite, Parasymplesite, Vivianite

Varieties:

Mg-rich Erythrite

Synonyms:

Arsenate of Cobalt, Cobalt bloom, Cobalt crust, Cobalt-mica, Cobalt Ocher, Erythrite (of Beudant), Red Cobalt, Red Cobalt ochre, Rhodoial

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Rarely well crystallized, typically flattened on [010], may be elongated prismatic and striated || [001], with many forms, to 10 cm. In radial or stellate aggregates, fibrous, drusy; usually powdery, massive.

Twinning:

None

Physical Properties

Cleavage:

Perfect on {010}; Poor on {100} and {102}

Fracture:

Conchoidal to Irregular/Uneven

Tenacity:

Sectile, flexible in thin {010} laminae

Moh's Hardness:

1.5 - 2.5

Density:

3.06 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Other:

Soluble in acids.

Optical Properties

Color:

Crimson to Peach-Red, pale Rose, or Pink, may be zoned.

Transparency:

Transparent to Translucent

Luster:

Sub-Adamantine, Pearly on {010} cleavages; Dull to Earthy as aggregates or massive

Refractive Index:

1.626 - 1.701  Biaxial  ( + ); may be Biaxial  ( - )

Birefringence:

0.0730

Dispersion:

r > v

Pleochroism:

Visible; X = pale pinkish to pale rose; Y = pale violet to pale violet-rose; Z = deep red.

Occurances

Geological Setting:

A secondary mineral in the oxide zone of some Co–Ni–As-bearing mineral deposits.

Common Associations:

Cobaltite, Skutterudite, Symplesite, Roselite-beta, Scorodite, Pharmacosiderite, Adamite, Morenosite, Retgersite, Malachite.

Common Impurities:

Ni ,Fe, Zn

Type Locality:

Daniel Mine (St. Daniel Mine), Neustädtel, Schneeberg District, Erzgebirge, Saxony, Germany

Year Discovered:

1832

View mineral photos:

Erythrite Mineral Photos and Locations

More Information

Mindat.org 
Webmineral.com

Erythrite is a beautifully bright red-purple colored mineral known as "cobalt bloom" by miners since it is very noticable and was used to spot veins of cobalt-bearing ore. It is a weathering product of cobalt containing minerals such as Cobaltite. Most Erythrite is found in the form of crusts, but larger crystals have been found at mines in the Bou Azzer district of Morocco. Erythrite gems are very rare and difficult to cut due to its very soft nature (Mohs 1.5 - 2.5) and perfect cleavage.

There are many localities for finding Erythrite, but few of importance. In France, at Chalanches, near Allemont, Isère. In Germany, fine examples with large crystals from Schneeberg, Saxony, at Wittichen, Black Forest, from Richelsdorf, Hesse, and elsewhere. At Jáchymov (Joachimsthal), Czech Republic. In the Botallack mine, St. Just, and from a number of other places in Cornwall, England. Larger crystals from the Aghbar (Arhbar), Irhtem (Ightem), and other mines in the Bou Azzer district, Morocco. From Cobalt, Ontario, Canada. In the USA, at the Blackbird mine, Lemhi County, Idaho. From the Sara Alicia mine, near Alamos, Sonora, Mexico. In Australia, from Mt. Cobalt, 110 km south of Cloncurry, Queensland, and at the Dome Rock copper mine, about 40 km northwest of Mingary, South Australia.
 

  
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