Colorless, Yellow, Blue, Reddish, Black, Reddish, Brown, Blue, gray, Black, Reddish, Brown, Blue, gray
Blue, Yellow, Brown, gray, Reddish, Greenish
Subconchoidal, Conchoidal, Brittle, ConchoidalArthur Thomas, Gemstones (2009)
(e.g. graphite).
Perfect on [001] and [011]
{???} Imperfect, {???} Imperfect