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Alleghanyite crystals up to 2 mm in size in a mixed franklinite/calcite/willemite block of 11×6.5×4 cm size. Location: Sterling Mine, Sussex County, New Jersey, US.
Category Nesosilicates
Humite group
(repeating unit)
Strunz classification 9.AF.45
Dana classification 52.3.2b.1
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group P21/a
Unit cell a = 10.46, b = 4.86
c = 8.3 [Å]; β = 109.133°; Z = 2
Formula mass 492.87 g/mol
Color Brown, bright pink, grayish pink, white
Crystal habit Granular; anhedral to subhedral crystals in matrix
Cleavage None
Fracture Conchoidal
Tenacity Brittle
Mohs scale hardness 5–6
Luster Vitreous
Diaphaneity Transparent to translucent
Specific gravity 4 (meas.), 4.11 (calc.)
Optical properties Biaxial (-)
Refractive index nα = 1.756
nβ = 1.78
nγ = 1.792
Birefringence 0.036
2V angle 72° (meas.), 68° (calc.)
Other characteristics Non-fluorescent
References [1][2]

Alleghanyite is a moderately rare humite mineral with formula Mn5(SiO4)2(OH)2, belonging to the nesosilicates class. In general its occurrences are related with metamorphic (metamorphosed) manganese deposits. The mineral is named after Alleghany County, North Carolina, US.[1]

See also[edit]


  1. ^ a b Alleghanyite. Mindat
  2. ^ Alleghanyite. Webmineral