39EARTHTypes of mineral The common
minerals that make up Earth’s
crust are called “rock-
forming minerals.” They
are mostly compounds of
the elements silicon and
oxygen. Other minerals
are “ore minerals”—
they contain large
amounts of mainly
metallic elements that
are very useful to us.
DIAMOND
is made of pure
carbon. It is the
hardest mineral
on Earth. GALENA is the
name given to lead
sulfide. Its crystals are
cubic in shape. If it is
hit with a hammer, the
crystals break off into
smaller cubes.WHAT USE IS A MINERAL?
Minerals have a huge range
of practical uses...
OThey can be mined to
extract metals (for example,
copper, gold, or silver).
OMinerals like potash and apatite can
be used as plant fertilizers.
OCrystals can be cut and polished into
gemstones (diamond, ruby, emerald).
OColored minerals are used as pigments.
OSome minerals are used in bath or
beauty products. CHALCOPYRITE
is a copper and iron
sulfide ore seen here
mixed with clear
quartz crystals.Minerals
When Earth first formed, it inherited many
different chemical elements. Over billions
of years, these elements combined to form
thousands of different chemical compounds.
WHAT IS A MINERAL?
Minerals are the building blocks
of every type of rock. They consist
of a single chemical element or
a compound of mixed elements.
There are about 4,000 different
minerals, but only 100 occur in
any great quantity.
How minerals form Most
minerals form when molten
rock or a hot solution cools and
forms crystals. The crystals that
form are affected by pressure
and temperature, so a mineral
can look different depending
on how it crystallizes. However,
some minerals, such as coal and
chalk, start off as living
organisms.Most minerals are crystals. The atoms in
the minerals are arranged in regular
patterns, which give crystals their simple
geometrical shapes. The crystal structure
affects many of the mineral’s
physical properties, such as
hardness, and how the
crystal fractures.CRYSTALS
CINNABAR is a sulfide
of mercury that forms
hexagonal crystals.