Color is one of the most
obvious properties of a
mineral but it is often of
limited diagnostic value,
especially in minerals
that are not opaque.
Never use color as a
final diagnostic
property.
Luster
metallic luster
look like a metal
Vitreous luster
is like that of glass, shiny and translucent to
transparent. Remember that glass can be almost any
color, including black, so don't be fooled by the color
pearly luster
have an
appearance
similar to a
pearl
earthy
luster
look like earth,
or dirt
waxy luster
look like paraffin,
typically
translucent but
dull
Streak
Streak is obtained by
scratching the mineral on an
unpolished piece of white
porcelain called a streak plate.
Because the streak plate is
harder than most minerals,
rubbing the mineral across the
plate produces a powder of
that mineral. Streak is
commonly more reliable than
color for identification.
Streak refers to the color of the
mineral in its powdered form,
which may or may not be the
same color as the mineral.
Streak is helpful for identifying
minerals with metallic or earthy
luster, because (with a few
exceptions) minerals with
nonmetallic luster generally
have a colorless or white streak
that is not diagnostic.
Hardness
Hardness is the resistance of a
mineral to scratching or abrasion
by other materials. Hardness is
determined by scratching the
surface of the sample with another
mineral or material of known
hardness. The standard hardness
scale, called Mohs Hardness Scale
consists of ten minerals ranked in
ascending order of hardness with
diamond, the hardest known
substance, assigned the number
10.
Cleavage and Fracture
Density
Density= m/v
Chemical Properties
Reaction with Acid
Some minerals,
especially
carbonate minerals,
react visibly with
acid. (Usually, a
dilute hydrochloric
acid [HCl] is used.)
Taste, Odor
Some minerals have a
distinctive taste (halite is
salt and tastes like it).
Some a distinctive odor
(the powder of some
sulfide minerals, such as
sphalerite, a zinc sulfide,
smells like rotten eggs).
Additional Properties
Special properties help
identify some minerals.
These properties may
not be distinctive
enough in most minerals
to help with their
identification. or they
may be present only in
certain minerals.
Magnetism
Some minerals are
attracted to a hand
magnet. To test a
mineral for
magnetism, just put
the magnet and
mineral together and
see if they are
attracted.
Refringence
The rays of light deviate
from their trajectory
when they pass through
a transparent mineral.
In some minerals, the
ray of light splits in two
(duplication of the
image), a property
known as birefringence.