A. Can be scratched by a fingernail
Cerargyrite Shiny white or Appears waxy; 1-1½
gray knife cuts it
smoothly; turns
violet brown to
black when
exposed to light
Gypsum White Soft; occurs as 2
crystals or as
fibrous,
granular,
compact, or
earthy masses
Talc White Knife cuts it 1
smoothly; feels
soapy or greasy;
splits into thin
flakes
B. Cannot be scratched by a fingernail but can be scratched by a copper
penny
Anhydrite White Commonly occurs 3-3½
as sugary-looking
masses
Barite White Rather heavy; 3-3½
cleavage
fragments may be
flat and slab-like
Calcite White Dilute 3
hydrochloric acid
fizzes on
calcite; perfect
cleavage in 3
directions gives
rhomb-shaped
fragments
Celestite White Not quite as 3-3½
heavy as barite;
crystals commonly
prism-shaped or
flat-looking;
some cleavage
fragments are
flat and slab-like
Halite White Salty taste; 2½
dissolves in
water;
cube-shaped
cleavage fragments
C. Cannot be scratched by a copper penny but can be scratched by an
ordinary pocket knife
Anhydrite White Commonly occurs 3-3½
as sugary-looking
masses
Barite White Rather heavy; 3-3½
cleavage
fragments may be
flat and slab-like
Celestite White Not quite as 3-3½
heavy as barite;
crystals commonly
prism-shaped or
flat-looking;
some cleavage
fragments are
flat and slab-like
Dolomite White Commonly occurs 3½-4
as granular
masses and as
rhomb-shaped
crystals; dilute
hydrochloric acid
may fizz slightly
on dolomite
Fluorite White Cleavage in 4 4
directions can
give fragments
that are shaped
like octahedrons;
crystals commonly
cubes
Opal White Curved, 5-6
conchoidal
fracture; may
appear glassy,
greasy, resinous,
or dull; milky
white and
bluish-white
precious opal
shows plays of
colors
D. Cannot be scratched by an ordinary pocket knife but can be scratched
by quartz
Feldspar White Glassy or pearly 6
luster; good
cleavage in 2
directions that
meet at an angle
of 90° or near
90°; common in
granite and
pegmatite rocks
Opal White Curved, 5-6
conchoidal
fracture; may
appear glassy,
greasy, resinous,
or dull; milky
white and
bluish-white
precious opal
shows plays of
colors
Quartz White Curved conchoidal 7
fracture; occurs
as milky quartz,
chert, and
chalcedony;
crystals commonly
6-sided prisms
with pyramid-like
ends