Mineral Properties
READING
WORKSHEET
To meet the definition of "mineral" used by most geologists, a substance must meet five
requirements. It must be naturally occurring, inorganic, a solid, have a definite chemical
composition, and an ordered internal crystalline structure. Minerals are identified by their physical
properties. A physical property is something you can see, feel, taste, touch, or smell. Remember
during our metal’s unit, we learned about ductile, malleable, and metallic luster. You will learn to
identify many common minerals by testing these properties in our investigations.
Luster is the way light is reflected from the mineral. It can be metallic, which is shiny
like a metal; or it can be nonmetallic and appear earthy, chalky, dull, glassy, or pearly.
Another way to identify a mineral is by the color of its streak. When the mineral is scraped
across a porcelain tile, it leaves a certain color powder behind. This color may be different than
the color of the mineral itself. For example, the mineral pyrite looks like gold. It is a golden color,
but it leaves a greenish-black streak. This is a great way to tell if you have found actual gold, or
just a piece of “fool’s gold.”
An important way to identify a mineral is by its hardness. Hardness is a measure of the
ease with which a smooth surface of a mineral can be scratched. It is also referred to as the
scratch test. The Mohs’ Scale of Hardness was developed to help identify common minerals. A
German scientist named Friedrich Mohs developed this system for comparing the hardness of a
mineral to ten common minerals. Mohs’ scale is based on common minerals, not on exact
differences in hardness. The difference in hardness between minerals two and three is much
less than the difference in hardness between minerals nine and ten. Even though the scale is
not exact, it is useful for identifying mineral specimens.
For instance, Talc is a mineral that is so soft you can pinch it into powder with your
fingers. Diamonds are the hardest minerals found on earth and are able to cut glass. A harder
mineral can scratch a softer one. Each mineral on the scale can scratch a mineral with a lower
number. Your fingernail has a hardness of about 2.5. A fingernail can scratch talc and gypsum,
but not calcite.
You can also look at how a mineral is broken. Cleavage is breakage along smooth, flat
planes. These breaks occur along planes of weakness in the mineral's structure.
However, if a mineral would break along an irregular surface, it does not have cleavage. (An
example of good cleavage would be muscovite or most quartz.) If a mineral were to fracture,
then it would have a rough, irregular surface. The breaks can be described as grainy, hackly
(jagged), conchoidal (curved), or splintery. (An example of this would be Rose quartz, even
though most quartz does have smooth cleavage.)
You can also use color. Some minerals are usually one color, but some can be different
colors. For instance, quartz has many colors. You cannot identify a mineral by color alone, but it
can sometimes be a useful property help identify certain minerals.
Mineral Properties
READING
WORKSHEET
Another way to identify minerals is by looking at the crystalline structure. This is a
repeating pattern in which the atoms line up. Does it have a crystal-like shape or grainy fibers?
Is it an octahedron?
And finally, some minerals have other special characteristics by which they can be
identified. The way they taste, smell, or the way they react with another substance may be a way
to identify the mineral. The mineral halite, for example, tastes salty.
Calcite will react with a mild acid, such as vinegar, to produce bubbling.
Remember, testing the properties of a mineral, is how we will identify unknown
minerals.
Reading Check: Fill in the blanks blanks with the correct word.
use your reading for the answers.
1. Minerals are identified by their ___________
.
2.A mineral must be naturally occurring, _______
, solid, have a definite
chemical composition, and an orderly crystalline structure.
3. ________ ___
is the way light is reflected from the mineral.
4. When the mineral is scraped across a porcelain tile, it leaves a certain
color powder behind. This is called a mineral’s ____________ .
5. ________________ is a measure of the ease with which a smooth surface of
a mineral can be scratched.
6. The Mohs’ Scale of Hardness was developed to help identify ___________
by a German scientist named Friedrich Mohs.
7.These breaks occur along planes of weakness in the mineral's structure are
called
.
8.If a mineral were to,
surface.
then it would have a rough, irregular
9.You cannot identify a mineral by _____________
a useful property help identify certain minerals.
10. ___________________
line up.
alone, but it can sometimes be
is a repeating pattern and a way that the atoms