phosphates
Erythrite
Co3(AsO4)2·8H2O
- Also known as
- cobalt bloompeach blossom ore
- Crystal system
- monoclinic
- Hardness
- 1.5–2.5 on the Mohs scale
- Lustre
- vitreous
- Colour
- Crimson to purple-pink
- Where it forms
- By weathering of cobalt arsenide ores, as a crust or bloom on the surface of altered material.
- Chiefly from
- Bou Azzer, MoroccoOntario, CanadaGermany
Why it is that colour
Cobalt. Erythrite is a cobalt arsenate and the pink is the cobalt.
Safety
A hydrated cobalt arsenate. Arsenic, plus cobalt, in a very soft mineral that crumbles readily. Do not handle it more than necessary, do not powder it, wash your hands, and keep it away from water and from food.
Where it comes from
Moroccan material from Bou Azzer is the classic source. Cobalt more generally is the subject of serious concern: the Democratic Republic of the Congo supplies the majority of world cobalt, artisanal mining there has been repeatedly documented as involving children and as lethally unsafe, and demand is driven by lithium-ion batteries.
Historical use
Its old name, cobalt bloom, reflects its use as a prospecting guide — a pink crust on the rock meant cobalt arsenide beneath. The word cobalt itself comes from the German kobold, a goblin, blamed by Saxon miners for ore that looked like silver, yielded none, and made them ill when smelted. The illness was arsenic.
Recorded as history and attributed where possible. That a stone was used for something establishes that people used it, not that it worked.
Worth knowing
The etymology of cobalt is a genuine piece of occupational history. Saxon miners in the Middle Ages found ore that looked like silver, produced nothing on smelting, and released fumes that made them sick. They blamed a mine goblin, the kobold, and the name stuck to the metal.
The fumes were arsenic trioxide, driven off from the cobalt arsenides. The miners were not being superstitious about a nothing; they had correctly identified that a particular ore was harming them and had explained it with the framework available. The explanation was wrong and the observation was right, which is a more interesting failure than simple credulity.
Identity checked against IMA-CNMNC master list, June 2025.