What is a mineral?
• A naturally occurring, inorganic solid that
has a crystal structure and a definite
• More than 3,000 identified minerals.
• About 20 minerals make up most of the
Characteristics of a mineral
1. Naturally occurring
4. Crystal structure
5. Definite Chemical composition.
• Mineral must occur naturally on Earth
– Gold, copper, silver, graphite
• The mineral cannot arise from materials
that were once part of a living thing
• Coal occurs naturally in the Earth’s crust,
but it comes from the remains of plants
and animals that lived millions of years
• A mineral is always solid, with a definite
volume and shape.
• The particles of a
mineral line up in
a pattern that
repeats over and
• A crystal has flat
faces, that meet
at sharp edges.
Definite Chemical Composition
• A mineral always contains certain
elements in definite proportions
– For example, the mineral of quartz has one
atom of silicon for every to atoms of oxygen.
How do we identify a mineral?
• Each mineral has its own specific
properties that can be used to identify it.
• In 1812, Friedrich Mohs, a mineral expert,
invented a test to describe and compare
the hardness of minerals.
• The scale ranks ten minerals from softest
• A mineral can scratch any mineral softer
• Color can be used to identify only those few
minerals that always have their own
– Malachite is always green
– Azurite is always blue
• Many minerals, however, like quartz, can occur
in a variety of colors.
• A streak test can provide a clue to a
• The streak of a mineral is the color of its
• You can observe a streak by rubbing a
mineral against a streak plate.
• Luster is the way a mineral reflects light
from its surface.
• Minerals containing metals are often shiny.
• Other minerals, such as quartz, have a
• No matter what the size of a mineral, the
density of that mineral always remains the
• You must determine the mass of the mineral
(on a balance)
• You then place the mineral in water, to see
how much it displaces.
• The volume of the displaced water, equals
the volume of the mineral.
Rocks mass = 300 ounces
Displaces water by 100 cm3
So volume of rock must be 100
D = MU 300
D = 100 g/cm3
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