A. Cannot be scratched by a fingernail but can be scratched by a copper
penny
Biotite (black mica) White Splits into thin, 2½-3
flat sheets that
will bend without
breaking
B. Cannot be scratched by an ordinary pocket knife but can be scratched
by quartz
Garnet White Commonly occurs 6½-7
as crystals
Quartz White Curved conchoidal 7
fracture;
brownish-black
smoky quartz
crystals commonly
6-sided prisms
with pyramid-like
ends;
_chalcedony_ and
_chert_ may be
black, too
Tourmaline White Black variety is 7-7½
_schorl_; notice
hardness,
striations on
crystals, and
triangular cross
section of some
crystals
C. Cannot be scratched by quartz
Tourmaline White Black variety is 7-7½
_schorl_; notice
hardness,
striations on
crystals, and
triangular cross
section of some
crystals