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

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.