Rare lead, copper chromate arsenate hydroxide mineral
Fornacite Dioptase (blue green), cerussite (light pink) and fornacite (green) from Renéville,
Djoué , Brazzaville Region, Republic of Congo
Category Arsenate mineral Formula (repeating unit) Pb2 Cu(CrO4 )(AsO4 )(OH) IMA symbol For[ 1] Strunz classification 7.FC.10 Dana classification 43.4.3.2 Crystal system Monoclinic Crystal class Prismatic (2/m) (same H-M symbol ) Space group P2 1 /cUnit cell a = 8.101(2), Color Deep olive-green Crystal habit Aggregates of steep pyramidal to bladed, rounded crystals Fracture Irregular/uneven, conchoidal, sub-conchoidal Tenacity Brittle Mohs scale hardness 2–3 Luster Resinous, waxy, greasy Streak Olive green Diaphaneity Transparent Density 6.27 g/cm3 Optical properties Biaxial (+) Refractive index nα = 2.142 nγ = 2.242 Birefringence δ = 0.100 2V angle Large References [ 2] [ 3] [ 4]
Fornacite is a rare lead , copper chromate arsenate hydroxide mineral with the formula: Pb2 Cu(CrO4 )(AsO4 )(OH). It forms a series with the phosphate mineral vauquelinite .[ 3] monoclinic – prismatic crystal system. It has a Mohs hardness of 2.3 and a specific gravity of 6.27.
It was first described in 1915 and named after Lucien Lewis Forneau (1867–1930) the governor of the French Congo. Its type locality is in Reneville, Republic of Congo .[ 3]
It occurs in the oxidized zone of ore deposits and is associated with dioptase , wulfenite , hemihedrite , phoenicochroite , duftite , mimetite , shattuckite , chrysocolla , hemimorphite , willemite and fluorite .[ 2]
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