Rocks and Minerals STUDY GUIDE
MINERALS
There are four basic characteristics of minerals
(SNIC). All minerals are…
 Solid
 Natural (not man made)
 Inorganic (not alive and never was)
 Crystalline structure- the atoms in minerals
are arranged in a geometric pattern that is
repeated.
A natural mineral deposit that is large enough
and pure enough to be mined for profit is
called an ore.
MINERAL IDENTIFICATION
Mineral identification refers to the way to tell
one mineral from another.
Color is the most obvious, but the least reliable
methods of identifying minerals because some
minerals are the same color and color can be
changed by the environment.
Luster describes how light is reflected from a
mineral’s surface. Luster can be described as
metallic or non-metallic.
Streak is the color of the mineral when it is
broken up into powder. The mineral is rubbed
on a "streak plate", which is a piece of
porcelain. When the mineral is rubbed across
the streak plate some of the mineral is broken
off and ground into a powder. Streak is more
accurate than color because it shows the true
color of the mineral.
Hardness is a measure of how easily a mineral
can be scratched. The Mohs Hardness Scale
lists hardness of ten minerals with (talc)1 being
softest and (diamond)10 the hardest.
Cleavage & Fracture refer to the way the
mineral breaks.
Cleavage refers to the tendency to split or
crack along parallel or flat planes.
Fracture occurs when a mineral breaks at
curved or irregular surfaces.
Volume is the amount of matter in a given
space. Mass divided by volume is density.
Specific gravity is another name for density.
ROCKS
The three main rock classifications are Igneous,
Sedimentary, and Metamorphic. Rocks can
change from one type to another through
various processes over millions of years.
Rocks are classified into these groups by the
way they were formed.
In order to identify a rock, you must determine
its mineral content.
90% of all rocks contain silicon and oxygen and
are called silicates. Rocks that do not contain
both oxygen and silicon are called non-silicates.
IGNEOUS
Igneous rock is formed from molten material
from a volcano (lava) or from deep inside the
earth (magma) which cools and hardens. “Igni”
is Latin for fire.
Extrusive Igneous Rock is formed when lava
cools quickly at the surface to form small
crystals. Rocks formed in this way have a fine –
grained texture. Examples of extrusive igneous
rocks are Pumice, Basalt, and Obsidian. When
lava erupts and cools in the ocean, it forms
new land.
Intrusive Igneous Rock is formed when magma
cools inside the earth. Rocks formed this way
have large crystals. They have a coarse –
grained texture. Granite is an example of an
intrusive igneous rock.
SEDIMENTARY
Sedimentary rock form when sediment is
compacted and cemented.
They form in in flat layers or strata. Fossils are
found in these layers.
Compaction occurs when small sediments are
pressed together.
Cementation occurs when the sediments are
glued together by minerals deposited between
the sediments.
Examples: Shale, Sandstone, limestone
METAMORPHIC
Metamorphic rocks form when any rock is
pushed down in the Earth and exposed to heat,
pressure, and chemicals.
Examples: shale becomes slate; limestone
becomes marble
IGNEOUS
Igneous rocks start as magma.
Igneous rocks forms when magma (molten rock
under the surface) and lava (molten rock on
the surface) cools and hardens into igneous
rock.