Alleghanyite

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.^[2]

Alleghanyite
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.
General
Category	Nesosilicates Humite group
Formula	Mn5(SiO4)2(OH)2
IMA symbol	Alh[1]
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
Identification
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	[2][3]

See also

• Chondrodite
• Clinohumite
• Humite
• Jerrygibbsite