Introduction to Mineralogy. Mineral Properties. What is a Mineral? It is a homogenous solid, inorganic, naturally occurring, with a definite chemical composition and highly structured atomic arrangement.

1. Minerals
a naturally occurring, inorganic,
homogenous solid with a definite
(but sometimes slightly variable)
chemical composition and a highly
structured atomic arrangement.

2. naturally occurring:
will distinguish between those
materials that are synthetically
produced in a laboratory and
those that are created by
natural processes.

3. All minerals are produced
from various processes that
are independent of living
organisms and thus are
inorganic.

4. Homogenous solid:
refers to the mineral’s
consistency throughout its
mass and is neither liquid nor
gas. Meaning that the mineral
cannot be further subdivided
into mineralogical
components.

5. Chemical Composition:
minerals can have alternative
element constituents as part
of its chemical formula.
Generally, these variations are
slight and the mineral is able
to maintain its identity.

6. Highly structured atomic
arrangement:
This indicates that there is an
ordered framework of atoms
building the mineral.

7. Physical Properties
• Mechanical Properties
Hardness
The hardness of a
mineral is its resistance
to scratching or
abrasion. Every mineral
can
be tested for its
hardness by either
Moh’s Hardness Scale
or by a relative
hardness scale.
Moh’s Hardness
Scale
• 1 talc 6 felspar
• 2 gypsum 7 quartz
• 3 calcite 8 topaz
• 4 flourite 9
corundum
• 5 apatite 10
diamond

8. There is also a relative hardness
scale that can be used in
conjunction with the above
scale. The items on this scale are
common objects that can be used
in testing the minerals.
fingernail 2.2 glass plate 5.5
new penny 3.2 streak plate 7
steel nail 5

9. Talc
Talc is the
softest mineral
on the Mohs
scale. This
softness makes
it very useful.
Soapstone is
made mainly of
talc and is
often carved
into decorative
shapes.
Corundum
Corundum is better
known by other
names-blue corundum
is called sapphire, red
corundum is called
ruby. Second only to
diamonds in hardness,
corundum is made into
valuable jewelry and
tools like emery
boards. It can scratch
every mineral but
diamond.

10. The cleavage of a mineral is its
tendency to break along weakened
planes within the
mineral. These areas of weakness
are a result of weak chemical
bonding within the atomic
arrangement of the crystal.
Cleavage

11. Cleavage:

12. Cleavage Directions
Angle Mineral Examples
• basal 1 - micas,
graphite
• prismatic 2 ~60 or ~90
pyroxene, amphibole
• rhombohedral 3 not 90
calcite, dolomite
• cubic 3 90 halite,
galena
• octahedral 4 ~70 flourite
• dodecahedral 6 60
sphalerite

13. Fracture
If a mineral does not exhibit cleavage of any
type, then the mineral is said to fracture. The
fracture of a mineral refers to its breakage in
numerous random directions without any 3
repetition of a set pattern. Fracture will occur
in a mineral due to the internal chemical
bonding being fairly uniform throughout the
mineral’s mass. There are several terms for
fracture which include conchoidal, hackly,
and irregular.

15. Optical Properties
These properties are defined by the way
light interacts with the surface of the
mineral. These interactions include
absorption, refraction, reflection, and
transmission of light.

16. Color
The color of a mineral is not its most
reliable characteristic. In many
instances, the color of a mineral may
vary greatly. Impurities of trace amounts
of other elements present in the mineral
may cause the differential coloration.
For example, amethyst is merely quartz
with trace amounts of ferric iron.

17. Streak
• The streak of a mineral is a much more
reliable test than the color of a mineral.
The streak of a mineral is the
representation of that mineral in its
powdered form. This test allows several
of the chemical bonds to be broken.

18. Luster
• Luster is the way in which a mineral reflects light.
The two major divisions of luster are metallic and
nonmetallic. If a mineral has a metallic luster, then
most of the light that “hits” the mineral is reflected
back and is considered to be opaque. Nonmetallic
minerals interact with the light differently by
displacing a range of reflectivities and are
considered to be translucent to transparent.

19. Luster
• There are several terms used to
describe nonmetallic luster. They
pertain to the amount of reflectivity that
is displayed by the sample. Some of the
terms include adamantine,
resinous,vitreous, pearly, silky, greasy,
and earthy.

20. Taste
• Taste is only testable on those minerals that are
water-soluble. Tasting of every mineral sample is
not recommended as some minerals contain
arsenic and mercury and are poisonous. To taste
a mineral, simply wet the end of your finger, rub
the finger on the sample, and place the finger to
your tongue.

21. Magnetism
Magnetism is a fundamental property in
some minerals that occurs due to
unpaired electrons on certain atoms.
Magnetite, pyrrhotite, and some
samples of hematite, are attracted by a
small magnet.

22. Solubility in Acid
Some minerals will react with acid. The
most common use for acid is using
dilute hydrochloric acid on members of
the carbonate mineral group. Other
minerals will react with other acids and
with acids at various temperatures.