Tschermakite
A calcium-rich aluminous amphibole — the end-member behind much of hornblende's chemistry.
Intro adapted from Wikipedia (CC BY-SA).
Tschermakite is an IMA-recognized mineral species in the silicate class, with the chemical formula Ca₂(Mg₃Al₂)(Si₆Al₂)O₂₂(OH)₂.
It crystallizes in the monoclinic crystal system (space group C2/m). It is a member of the Amphibole structural group.
Key properties: Mohs hardness 5–6; specific gravity 3.15; [Vitreous.] luster; refractive index 1.653; optically biaxial.
IMA symbol Tsr, IMA status: approved, named in 1945.
From eclogites and other ultramafic igneous rocks, and in medium- to high-grade metamorphic rocks, typically amphibolites.
It is found associated with Kyanite, garnet.
The mineral was named to honor Professor Gustav Tschermak von Seysenegg (1836–1927), Austrian mineralogist, University of Vienna, Vienna, Austria.