The alpha polymorph of calcium silicate (Ca₂SiO₄). Larnite is a mineral which crystallizes at high temperature. Its occurrences are practically confined to limestone or chalk zones in contact with semimolten balsalts. The presence of magnesium leads to the formation of other structurally related high-temperature minerals such as merwinite (Ca₃Mg(SiO₄)₂), bredigite (Ca₇Mg(SiO₄)₄), and alite (Ca₃O(SiO₄)). These phases are structurally very dense and have been postulated as possible components in the Earth's mantle. At least four polymorphs of Ca₂SiO₄ are known, and a few others are stabilized by impurities. They often occur in silicate slags and clinkers.