Eritrina

Erythrite is a hydrated cobalt arsenate that forms as a secondary mineral in oxidation zones and is recognised by pink to magenta colours and acicular or prismatic habits.

It develops by secondary oxidation in deposits with Co–Ni–As minerals, often by alteration of arsenides. It crystallises in radial or prismatic aggregates and as acicular needles; the acicular habit, known as cobalt bloom, is less common than the tabular form. Spherulitic clusters and velvety botryoidal masses with silky lustre also occur. It is fragile and its lustre varies with the aggregate type.

Colour ranges from pale pink to fuchsia or carmine, with deep wine tones depending on cobalt concentration. It is a visual indicator of cobalt in a deposit. At Agoudal it forms flat, pointed crystals with silky lustre and deep wine colour, sometimes confused with roselite or anorthoroselite.

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