Earth Materials
The crust of the earth is its outer shell of
rock.
The most abundant elements in the crust are
oxygen (47% by mass) and silicon (28%);then come
aluminum, iron, calcium, sodium, potassium, and
magnesium, which range from 8% to 2% in that
order.
Since the O ion is relatively large, over 90% of
the volume of the crust is oxygen.
MINERALS
Rocks are aggregates of homogeneous substances
called minerals.
Commoner minerals or mineral groups are the
feldspars, quartz, the ferromagnesian minerals,
the clay minerals, and mica, which are all
silicates, and calcite, which is composed of
calcium carbonate.
Rocks are classified as igneous, sedimentary
and metamorphic.
IGNEOUS ROCKS
Igneous rocks cooled from a molten
state.
Two-thirds of crustal rocks are
igneous, with basalt constituting
the bedrock under the oceans and
granite the bedrock under the
continents.
Intrusive igneous rocks solidified
beneath the surface where slow
cooling resulted in large mineral
grains.
Extrusive igneous rocks solidified
after emerging from a volcano or
other vent, and the rapid cooling
resulted in small mineral grains
SEDIMENTARY ROCKS
Most sedimentary rocks are composed of fragments
of other rocks that have been eroded by the
action of running water, glaciers, or wind.
Sediments are usually deposited in layers.
Sedimentary rocks make up only about 8% of the
crust.
Three-quarters of surface rocks are of this kind.