Erythrite
Hydrated cobalt arsenate (Co3(AsO4)2 8H2O)
A soft pink to crimson hydrated cobalt arsenate, famous as cobalt bloom that signals nearby cobalt ores.
- Mohs hardness
- 1.5-2.5
- Color
- Crimson, pink, peach, purplish-red
- Type
- mineral
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Overview
Erythrite is a hydrated cobalt arsenate, Co3(AsO4)2 8H2O, instantly recognizable by its crimson, pink, and peach-blossom colors. It crystallizes in the monoclinic system and forms a series with nickel-rich annabergite, which is green.
Its name comes from the Greek word for red. Erythrite is best known as cobalt bloom, a soft powdery or crusty coating that forms on weathered cobalt minerals and serves as a visual prospecting guide to underlying ore.
Well-crystallized erythrite, with its bladed crimson crystals, is among the most beautiful of the secondary arsenate minerals and is highly prized by collectors.
Formation & geology
Erythrite is a secondary mineral that forms by the oxidation and weathering of primary cobalt arsenide minerals such as skutterudite, cobaltite, and nickeline in the upper, oxidized zones of ore deposits.
It occurs as crusts, earthy coatings, radiating crystal sprays, and bladed crystal groups lining cavities in weathered veins.
Outstanding crystallized specimens come from Bou Azzer (Morocco), which is the premier source, as well as Schneeberg (Germany), Cobalt (Ontario), and various European cobalt districts. Its bright color makes it an unmistakable indicator of cobalt mineralization.
How to identify it
Erythrite is identified by its distinctive crimson to pink, peach-blossom color, which is unlike almost any other mineral, along with a pearly to adamantine luster on crystal faces and a paler pink to red streak.
It is very soft (Mohs 1.5 to 2.5) and forms bladed, prismatic crystals, radiating sprays, or soft earthy crusts (the classic cobalt bloom).
Its unique color and association with cobalt arsenides make it hard to confuse with other minerals. The green nickel analog annabergite looks similar in form but differs in color. Heating releases a garlic-like arsenic odor.
Uses & significance
Erythrite itself is not mined as an ore, but its bright color makes it a valuable prospecting indicator, historically guiding miners to underlying cobalt and nickel arsenide ore bodies.
Its greatest value today is as a mineral specimen. Fine bladed crimson crystal groups from Bou Azzer, Morocco, are spectacular and highly sought after by collectors worldwide.
Because erythrite contains arsenic, specimens must be handled with care: avoid creating dust, do not ingest, wash hands after handling, and keep away from children. It has no practical industrial application.
Frequently asked questions
What is cobalt bloom?
Cobalt bloom is the common name for erythrite, the pink to crimson powdery coating that forms on weathered cobalt minerals and signals cobalt ore.
Where are the best erythrite crystals found?
Bou Azzer in Morocco is the world's premier source of fine bladed crimson erythrite crystals prized by collectors.
Is erythrite related to annabergite?
Yes, they form a series; erythrite is the cobalt (pink) member and annabergite is the nickel (green) member, with otherwise similar structure.
Is erythrite dangerous?
It contains arsenic, so handle it carefully, avoid dust and ingestion, wash your hands afterward, and keep it away from food and children.
Erythrite guides
In-depth guides for identifying, valuing, and understanding Erythrite.
Erythrite identified by the community
Real specimens identified with Rock Identifier.
