are classified by their origin, or how the rock was formed.
A. Rocks are classified by observing:
1. the COLOR of the rock
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
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)
a. Coarse grain
b. Fine grain
c. No grain
2. Grain Shape
a. smooth and rounded
or random grains resulting in banded or non-banded rock
Three major rock groups
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