posted on Jun, 7 2009 @ 05:09 PM
Quartz doesn't form cubic crystals however...they are more likely to be trigonal.
Minerals that crystallise into a cubic form include: halite, copper, gold, silver, platinum, iron, fluorite, leucite,diamond, garnet, spinel, pyrtie,
galena and magnetite.
Then there are cleavage planes (which can occur at right angles).
I'm curious. I'm going with 'rock' at this time, but can be swayed if there is enough supporting evidence for it being anything else.