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The Mineral erythrite

Radiating Erythrite Spray

Erythrite is a deeply colored reddish or pink mineral, with its distinctive color caused by its cobalt content. Erythrite is the end member of a series with Annabergite, with Erythrite being the cobalt-dominant member and Annabergite being the nickel-dominant member. Erythrite is named from the Greek erythros, red, in reference to the hue of this mineral.

Chemical Formula

Co₃(AsO₄)₂ · 8(H₂O)

Color

Deep purplish-red, hot pink, light pink, dark pinkish-red; sometimes with a bluish hue.

Crystal System

Monoclinic

Properties

Streak
Light red to pink

Hardness
1.5 - 2.5

Transparency
Transparent to translucent

Specific Gravity
3.0 - 3.2

Luster
Vitreous, pearly

Cleavage
1,1

Fracture
Splintery

Tenacity
Sectile and slightly flexible

Crystal Habits

Large crystals are uncommon; most often as fragile radiating, acicular, or fibrous groupings and encrusting. Also botryoidal, reniform, in rounded spiky balls, earthy, and massive. Individual crystals are elongated and usually thin and bladed, with a distinctly angled termination. Crystals are often striated.

Additional Information

Composition
Hydrous cobalt arsenate, sometimes with some nickel

In Group
Phosphates; Arsenates

Striking Features
Color, crystal habits, and streak.

Environment
As a secondary mineral that forms as an alteration of sulfides and arsenides in the oxidation zone of cobalt deposits. Also in hornfels of contact metamorphic rocks.

Rock Type
Sedimentary, Metamorphic

Other Names

	Cobalt bloom
	Red cobalt

Uses

Erythrite is an ore of cobalt, and is an important collectors mineral.

Noteworthy Localities

The classic type locality of Erythrite is the Schneeberg District, Saxony, Germany, where this mineral was found in bright radiating and acicular sprays on matrix. Until modern times, Schneeberg was considered to be the finest occurrence of this mineral. Good specimens from this locality are hard to come across today as most of the outstanding examples are in old and classic collections.

The largest Erythrite crystals ever found come from the Bou Azer district in Morocco. This region has been producing outstanding, vividly-colored masterpieces with beautiful color and form. Specific notable deposits in Bou Azer include the Aghbar Mine and the Agoudal Mine.

Other notable Erythrite occurrences are Mt. Cobalt, Queensland, Australia; the Sara Alicia Mine, near Alamos, Sonora, Mexico (hot pink fibrous acicular groups); and Cobalt, Timiskaming District, Ontario, Canada (pink crusts, sometimes associated with Silver).

The U.S. lacks significant Erythrite occurrences. Two localities that have produced small crusts are the French Creek Mines, St. Peters, Chester County, Pennsylvania; and the the Blackbird District, Lemhi Co., Idaho.