Monticellite and kirschsteinite (commonly also spelled kirschteinite Klein and Hurlbut ''Manual of Mineralogy'' 20th ed., p. 373) are

gray Grey (more common in British English) or gray (more common in American English) is an intermediate color between black and white. It is a neutral or achromatic color, meaning literally that it is "without color", because it can be composed o ...

silicate In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is al ...

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...

s of the olivine group with compositions Ca Mg Si O₄ and Ca FeSiO₄, 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

Italian Italian(s) may refer to: * Anything of, from, or related to the people of Italy over the centuries ** Italians, an ethnic group or simply a citizen of the Italian Republic or Italian Kingdom ** Italian language, a Romance language *** Regional Ita ...

mineralogist Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the proces ...

(1759–1845). Kirschsteinite is named after Egon Kirschstein, German geologist. Like other members of the group monticellite and kirschsteinite have

orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a r ...

unit cells (space group ''Pbnm'') shown in Figure 1. Iron and magnesium ions are located on the M1 inversion sites and calcium ions occupy the M2 site on mirror planes. The unit cell is somewhat larger than for the calcium free olivines

forsterite Forsterite (Mg2SiO4; commonly abbreviated as Fo; also known as white olivine) is the magnesium-rich end-member of the olivine solid solution series. It is isomorphous with the iron-rich end-member, fayalite. Forsterite crystallizes in the orthor ...

and

fayalite Fayalite (, commonly abbreviated to Fa) is the iron-rich end-member of the olivine solid-solution series. In common with all minerals in the olivine group, fayalite crystallizes in the orthorhombic system (space group ''Pbnm'') with cell para ...

with :''a'' = 0.4815 nm, :''b'' = 1.108 nm and :''c'' = 0.637 nm, and for monticellite :''a'' = 0.4875 nm, :''b'' = 1.1155 nm and :''c'' = 0.6438 nm.

Gallery

File:Atomic_structure_of_olivine_1.png, The atomic scale structure of olivine looking along the ''a'' axis. Oxygen is shown in red, silicon in pink, and Mg, Fe and Ca in blue. A projection of the unit cell is shown by the black rectangle. File:Kirschsteinite-111353.jpg, Colourless crystals of kirschsteinite

References

* Deer, W. A., Howie, R. A., and Zussman, J. (1992). ''An introduction to the rock-forming minerals (2nd ed.)''. Harlow: Longman
Mindat.org

Webmineral.com

Handbook of Mineralogy
Nesosilicates Orthorhombic minerals Minerals in space group 62 {{silicate-mineral-stub