Erythrite Identification Guide
Identify erythrite, the crimson cobalt bloom mineral, by its striking pink-purple color, softness, and association with cobalt and arsenic ores.
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What Erythrite Looks Like
Erythrite is a hydrated cobalt arsenate (Co3(AsO4)2.8H2O) famous as "cobalt bloom" - a vivid pink-to-crimson coating and crystal spray on weathered cobalt ores.
- Color: crimson, rose-pink, to purplish-red; diagnostic and rarely matched by other minerals.
- Luster: adamantine to vitreous on crystals; dull/earthy on crusts.
- Transparency: transparent to translucent on crystals; opaque as powdery coatings.
- Habit: flattened bladed or prismatic crystals in radiating sprays and "stars," plus earthy films and crusts on ore.
Step-by-Step Field-ID Checklist
- Note the color. An intense pink-to-crimson bloom on dark gray ore is the first clue.
- Check softness. Erythrite is very soft; a fingernail or copper coin marks crystals (Mohs ~1.5-2.5).
- Look at habit. Radiating bladed crystal sprays or velvety pink crusts are typical.
- Note the host. It coats cobalt and nickel arsenide ores (skutterudite, cobaltite, smaltite).
- Confirm streak. Streak is pink to pale red, matching the body color.
Key Diagnostic Tests
- Mohs hardness: 1.5-2.5 (very soft, scratched by a fingernail).
- Streak: pink to pale red.
- Cleavage: perfect in one direction (crystals split into thin flexible flakes).
- Specific gravity: ~3.1.
- Solubility/chemistry: soluble in hydrochloric acid giving a pink solution; contains arsenic, so wash hands and avoid inhaling dust.
- No magnetism.
Common Look-Alikes and How to Tell Them Apart
- Cobaltoan calcite: also pink but harder is not the rule; it fizzes in acid and lacks the crimson bladed crystals and arsenic chemistry.
- Rhodochrosite/rhodonite: harder (3.5-6.5), more rose-banded or massive, no association with arsenide ores.
- Roselite/other cobalt arsenates: can look similar; locality and crystal form help, and lab tests confirm.
- Pink fluorite: harder (4), cubic, and shows cubic cleavage rather than blades.
Where It Is Typically Found
Erythrite occurs in the oxidized zones of cobalt-nickel-arsenic deposits. Classic localities include Bou Azzer (Morocco) for fine crystals, Schneeberg (Germany), Cobalt, Ontario (Canada), and various Czech and Spanish mining districts. Prospectors historically used the pink bloom as a visual indicator of nearby cobalt ore.
Frequently asked questions
How can you tell if it's real erythrite?
Look for vivid crimson-to-pink bladed crystals or bloom on dark cobalt-arsenide ore, a pink streak, hardness around 1.5-2.5 (scratched by a fingernail), and one perfect cleavage. It does not fizz in acid like pink calcite.
What is cobalt bloom?
Cobalt bloom is the common name for erythrite, the pink-to-crimson hydrated cobalt arsenate that forms as a weathering coating on cobalt ores and signals cobalt nearby.
Is erythrite dangerous to handle?
It contains arsenic, so handle it carefully: avoid inhaling dust, do not lick or taste it, keep it away from food, and wash your hands after touching specimens.
Erythrite vs rhodochrosite: how are they different?
Rhodochrosite is a harder (3.5-4) banded pink carbonate that fizzes in warm acid. Erythrite is much softer, forms crimson blades on arsenide ore, contains arsenic, and does not effervesce.
Erythrite identified by the community
Recent Erythrite specimens identified with Rock Identifier.
