monticellite

{{Infobox mineral | name = Monticellite-Kirschsteinite | category = Nesosilicate | image = Monticellite-D1056b.jpg | imagesize = 260px | caption = Sharp, freestanding monticellite crystals to over 1 cm, perched on semilustrous brown vesuvianite (idocrase) crystals. Remnant calcite matrix is blue-gray. | formula = Ca(Mg,Fe)SiO4 | IMAsymbol = Mtc – Kir | molweight = | strunz = 9.AC.10 | system = Orthorhombic | class = Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) | symmetry = Pbnm | colour = colourless or grey | habit = | twinning = | cleavage = {010} | fracture = | mohs = 5.5 | luster = | refractive = α = 1.638 – 1.654, β = 1.646 – 1.664, γ = 1.650 – 1.674 | opticalprop = | birefringence = | pleochroism = | streak = | gravity = 3.05 – 3.27 | density = | melt = 1503 °C | fusibility = | diagnostic = | solubility = | diaphaneity = | other = | references = }}

Monticellite and kirschsteinite (commonly also spelled kirschteinite) are gray silicate minerals of the olivine group with compositions CaMgSiO4 and CaFeSiO4, respectively. Most monticellites have the pure magnesium end-member composition but rare ferroan monticellites and magnesio-kirschsteinite are found with between 30 and 75 mol.% of the iron end member. Pure kirschsteinite is only found in synthetic systems. Monticellite is named after Teodoro Monticelli, an Italian mineralogist (1759–1845). Kirschsteinite is named after Egon Kirschstein, a German geologist.