Larnite

Larnite is a calcium silicate mineral with the formula Ca₂SiO₄. It is the calcium member of the olivine group of minerals.

Larnite
General
Category	Nesosilicates
Formula (repeating unit)	Ca2SiO4
IMA symbol	Lrn^[1]
Strunz classification	9.AD.05
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/n
Unit cell	a = 5.5, b = 6.74 c = 9.29 [Å]; β = 94.59°; Z = 4
Identification
Color	White to gray
Crystal habit	Flattened anhedral grains; massive
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	^[2]

It was first described from an occurrence at Scawt Hill, Larne, Northern Ireland in 1929 by Cecil Edgar Tilley and named for the location.^[2] 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.^[2]

Dicalcium silicate is chemically β–Ca₂SiO₄, sometimes represented by the idealized oxide formula 2CaO·SiO₂ also noted C₂S in the cement chemist notation (CCN). When used in the cement industry, the mineral is usually referred to as belite.

References

1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
2. Larnite on Mindat.org

• Deer, William Alexander; Howie, R. A; Zussman, J (1986). "Larnite". Disilicates and ring silicates. pp. 248–249. ISBN 978-1-897799-89-5.