Rocks
Rocks are:
 A solid made of one
or more minerals and
other materials.
Identifying Rocks:
 Rocks are further
identified by:
 color
 texture
 mineral composition
Classifying Rocks:
 Rocks are classified
based on how they
were formed.
Texture:
 Texture is the quality
of a rock that is based
on the sizes, shapes,
and positions of the
rock’s grains.
Composition:
Identifying Rocks:
 Composition is the
chemical makeup of a
rock. Composition can
describe either the
minerals or other
materials in the rock.

 Rocks are further
identified by:
 color
 texture
 mineral composition
Grains:
Grain Size:
 Some rocks have grains that are
large and easy to see.
 These rocks are coarse grained.
 Other rocks have grains so small
they are microscopic.
 These are fine grained rocks.

 Particles of
minerals
that make up
a rock.
 Texture is
determined
by grain
size, grain
shape, and
grain
pattern.

Grain Pattern:
Grain Shape:





Grains can be:
fine sand
crystals
fragments that can
be smooth or jagged
 Grains can lie flat in layers
like a stack of pancakes.
 Some have patterns that look
like waves or swirls
 Some resemble rows of beads.
 Others will have random
patterns.

No Visible Grain:
 Some rocks resemble pieces of
glass.
 These rocks cooled very quickly
so crystals did not have time to
grow.
Mineral Composition:
 Since rocks are really
combinations of minerals,
geologists must slice their
samples into very thin pieces to
test which minerals are present.
Origin of Rocks:
 Rocks are
classified by
the way they are
formed.
 Igneous rocks:
formed from the
cooling of
molten rock.
 Sedimentary
rocks: formed
from sediments
being compacted
and cemented.
 Metamorphic
rocks: existing
rock that is
changed by heat,
pressure, or
chemical