Gems, Sixth Edition (2006), Gems, Sixth Edition (2006), Uneven
Conchoidal, Conchoidal, Gemstones of the world (2001) More from other references, Conchoidal, Brittle
From the Greek, oligos and kasein, little cleavage.
111 (perfect in four directions)
Na(90-70%)Ca(10-30%)(Al,Si)AlSi 2O 8Michael OâDonoghue , Gems, Sixth Edition (2006)
C