Zirkelite

Formula: (Ti,Ca,Zr)O_2-x

Origin of name: Named after Ferdinand Zirkel (1838-1912), professor of mineralogy, University of Leipzig (Germany). A pioneer in the microscopic investigation of rocks.

Crystal system: monoclinic, pseudocubic

Crystal class: 2/m

Twinning:

Unit cell: a = 12.43 Å, b = 7.22 Å, c = 11.48 Å, β=100.33°

Colour: black, dark reddish brown

Diaphaneity: opaque to subtranslucent

Luster: resinous

Habit: crystals pseudo-octahedral, flattened, twinned, pseudocubic

Hardness: 5.5

Specific gravity: 4.71 to 4.74

Cleavage: none

Tenacity: Brittle, conchoidal fracture

Streak: Brownish gray

Synonyms/varieties: Polymignite-metamict

Comments: dimorphous with calciobetafite. Found with baddeleyite in decomposed magnetite-pyroxenite.