Melanterite

sulphate

pyrite

Formula: Fe(SO4).7H2O sulphate
Specific gravity: 1.89
Hardness: 2
Streak: White
Colour: Colourless to white or green, also greenish-blue to blue with increased Cu content; colourless to pale green in transmitted light. Usually a yellowish-white after exposure to air and moisture.
Solubility: Readily soluble in water
Environments:

hydrothermal environments

Alteration

Melanterite is a secondary mineral formed by the oxidation of pyrite, marcasite and other iron sulphides in massive hydrothermal replacement deposits. It is often found in mines as a post-mining formation.
Melanterite may dehydrate to siderotil.

pyrite (primary) O and H2O to secondary melanterite and sulphuric acid.
FeS2 + 7O + 8H2O → FeSO4.7H2O + H2SO4
Melanterite indicates the presence of sulphuric acid, and it should be handled with care.

Common impurities: Cu,Mg

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