Classifying Rocks
Rocks
are classified by their origin, or how the rock was formed.
A. Rocks are classified by observing:
1. the COLOR of the rock
2.
the TEXTURE of the rock (How the rock surface looks and feels. For example, smooth and glassy)
a. depending on the size, grains can be observed using the
naked eye, hand lens, or a microscope.
3. the MINERAL COMPOSITION of the rock.
a. minerals can be identified by:
i) cutting the rock very thin and shinning light through it.
ii) chemical tests
iii) magnetic tests
B.
Rock Texture is a result of the SIZE, SHAPE, and PATTERN of GRAINS in the rock (grains are parts of other rocks, or
particles of minerals)
1. Grain
Size
a. Coarse grain
b. Fine grain
c. No grain
2. Grain Shape
a. smooth and rounded
b. jagged
3.
Grain Pattern
a. layered
or random grains resulting in banded or non-banded rock
C.
Three major rock groups
a.
Igneous - formed when molten material cools
b. Sedimentary - formed when sediment is pressed and cemented together over time
c. Metamorphic - formed when any rock undergoes
pressure and heat
