Larnite

Larnite
General
Category	Silicate mineral
Formula (repeating unit)	Ca2SiO4
Strunz classification	9.AD.05 Nesosilicates
Crystal symmetry	Monoclinic prismatic H-M symbol: (2/m) Space group: P 21/n
Unit cell	a = 5.5 Å, b = 6.74 Å, c = 9.29 Å; β = 94.59°; Z=4
Identification
Color	White to gray
Crystal habit	Flattened anhedral grains; massive
Crystal system	Monoclinic
Twinning	Common, polysynthetic parallel to {100}
Cleavage	Good on {100}, imperfect on {010}
Mohs scale hardness	6
Luster	Vitreous
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	3.28–3.33
Optical properties	Biaxial (+)
Refractive index	nα = 1.707 nβ = 1.715 nγ = 1.730
Birefringence	δ = 0.023
2V angle	74° calculated
Dispersion	r > v
References

Larnite is a calcium silicate mineral with formula: Ca₂SiO₄.

It was first described from an occurrence at Scawt Hill, Larne, Northern Ireland in 1929 by Cecil Edgar Tilley and named for the location. At the type locality it occurs with wollastonite, spurrite, perovskite, merwinite, melilite and gehlenite. It occurs in contact metamorphosed limestones and chalks adjacent to basaltic intrusives.

Dicalcium silicate is chemically, β–Ca₂SiO₄, sometimes represented by the formula 2CaO·SiO₂. When used in the cement industry, the mineral is usually referred to as belite.