Ferberite

Ferberite is the iron endmember of the manganese - iron wolframite solid solution series. The manganese endmember is hübnerite. Ferberite is a black monoclinic mineral composed of iron(II) tungstate, FeWO₄.

Ferberite
Ferberite with muscovite from Minas da Panasqueira, Beira Baixa, Portugal
General
Category	Tungstate mineral
Formula (repeating unit)	FeWO4
Strunz classification	4.DB.30
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P2/c
Unit cell	a = 4.72, b = 5.7 c = 4.96 [Å]; β = 90°; Z = 2
Identification
Color	Black, dark brown in transmitted light
Crystal habit	Bladed crystals; massive
Twinning	Contact or interpenetrant or lamellar twins
Cleavage	Perfect on {010}; partings on {100} and {102}
Fracture	Uneven
Tenacity	Brittle
Mohs scale hardness	4–4.5
Luster	Submetallic to metallic adamantine
Streak	Brownish black
Diaphaneity	Nearly to entirely opaque
Specific gravity	7.58
Optical properties	Biaxial (+)
Refractive index	nα = 2.255 nβ = 2.305 nγ = 2.414
Birefringence	δ = 0.159
2V angle	Measured: 66°
Other characteristics	Slightly magnetic
References	[1][2][3]

Ferberite and hübnerite often contain both divalent cations of iron and manganese, with wolframite as the intermediate species for which the solid solution series is named.[4]

Ferberite occurs as granular masses and as slender prismatic crystals. It has a Mohs hardness of 4.5 and a specific gravity of 7.4 to 7.5. Ferberite typically occurs in pegmatites, granitic greisens, and high temperature hydrothermal deposits.[1] It is a minor ore of tungsten.

Ferberite was discovered in 1863 in Sierra Almagrera, Spain, and named after the German mineralogist Moritz Rudolph Ferber (1805–1875).[2]

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  Twinned Ferberite, Tazna Mine, Atocha-Quechisla District, Nor Chichas Province, Potosí Department, Bolivia. 4.8 x 4.0 x 3.6 cm.
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  Ferberite - Cínovec / Zinnwald, Erzgebirge; Krusné Hory Mts, Saxony & Ústí Region (Bohemia), Germany & Czech Republic