Formula: CaFe4(PO4,SO4)2(OH)8 . 4-6H2O
Origin of name: For J. Delvaux de Feuffe (1782-1863), Belgian chemist, who first described and analyzed the mineral.
Crystal system: Amorphous
Crystal class: Unknown
Twinning:
Unit cell:
Colour: Yellowish brown to brown, reddish brown to brownish black
Diaphaneity:
Luster: Vitreous, greasy, weak waxy
Habit: Botryoidal crusts, concretionary masses and stalactites; gel-like
Hardness: 2.5 to 4
Specific gravity: 1.85 to 2.83
Cleavage: None
Tenacity:
Streak: Yellow
Synonyms/varieties: borickite, foucherite
Comments:
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