Tilleyite Locality: Crestmore quarries, Crestmore, Riverside County, California, USA Original description: A 4.3 by 4.0 cms mass. JSS specimen and photograph. — Photo: John Sobolewski (JSS) · CC BY 3.0
Tilleyite
A rare calcium silicate-carbonate of contact-metamorphosed limestones.
Intro adapted from Wikipedia (CC BY-SA).
Tilleyite is an IMA-recognized mineral species in the silicate class, with the chemical formula Ca₅Si₂O₇(CO₃)₂.
It crystallizes in the monoclinic crystal system (space group P2_1/a).
Key properties: specific gravity 2.82–2.84; Dull luster; optically biaxial.
IMA symbol Tly, grandfathered status — known before the IMA’s founding, named in 1933.
Found in the contact metamorphic zone between igneous rocks and limestones, formed at low pressure and high temperature.
It is found associated with Merwinite, spurrite, gehlenite, vesuvianite, grossular, wollastonite, thaumasite, fluorite, calcite.
The name refers to Cecil Edgar Tilley (1894–1973), British petrologist, Cambridge University, Cambridge, England.