Babingtonite

Babingtonite
Triclinic crystals of babingtonite with prehnite, from Qiaojia, Qiaojia Co., Zhaotong, Yunnan, China (size: 71 mm x 55 mm, 71 g)
General
Category	Inosilicate
Formula (repeating unit)	Ca2(Fe,Mn)FeSi5O14(OH)
Strunz classification	9.DK.05
Crystal system	Triclinic
Crystal class	Pinacoidal (1) H-M symbol: (1)
Space group	P1
Identification
Color	Dark green to black
Crystal habit	Prismatic crystals
Cleavage	Perfect on {001}, Good on {010} and {100}
Fracture	Irregular/uneven
Tenacity	Brittle
Mohs scale hardness	5.5 to 6
Luster	Vitreous
Diaphaneity	Translucent on thin edges, opaque
Specific gravity	3.3
Refractive index	nα= 1.700 nβ= 1.710 nγ= 1.725
Birefringence	δ = 0.025
Pleochroism	Visible
Dispersion	r > v strong
References

Babingtonite is a calcium iron manganese inosilicate mineral with the formula Ca₂(Fe,Mn)FeSi₅O₁₄(OH). It is unusual in that iron(III) completely replaces the aluminium so typical of silicate minerals. It is a very dark green to black translucent (in thin crystals or splinters) mineral crystallizing in the triclinic system with typically radial short prismatic clusters and druzy coatings. It occurs with zeolite minerals in cavities in volcanic rocks. Babingtonite contains both iron(II) and iron(III) and shows weak magnetism. It has a Mohs hardness of 5.5 to 6 and a specific gravity of 3.3.

It was first described in 1824 from samples from Arendal, Aust-Agder, Norway (which is its type locality) and was named after the Irish physician and mineralogist William Babington (1757–1833).

It is the official mineral (mineral emblem) of the Commonwealth of Massachusetts.

References

• Mineral galleries

Babingtonite (dark) on Prehnite, Qiaojia, Qiaojia County, Yunnan Province, China . Crystal is 1.3 cm. high