Fassaite

Fassaite is a variety of augite with a very low iron content, Ca(Mg,Fe,Al)(Si,Al)₂O₆.^[2] It is named after the Fassa Valley, Italy.

Fassaite
Fassaite from Val di Fassa
General
Category	Minerals
Formula	Ca(Mg,Fe,Al)(Si,Al)2O6
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/c (no. 15)
Identification
Color	light-dark green, black
Crystal habit	prismatic, short, plane
Mohs scale hardness	6
Streak	greenish-white
Specific gravity	2.9-3.3
References	[1]

It is thought to be a contact mineral formed at high temperature on the interface between volcanic rocks and limestone. It is also reported in meteorites.^[3]