Download Metamorphic Igneous Sedimentary 3 Major Groups of Rocks

Locations of Rocks in Texas
•Dallas
•El Paso
Guadalupe Mountains
•Austin
•Houston
Type of rock
Igneous
Metamorphic
Sedimentary
Metamorphic
and Sedimentary
Igneous and
Metamorphic
Color
Rock-forming and rock-destroying processes have been active for billions of years. Today, in the
Guadalupe Mountains of western Texas, one can stand on limestone, a sedimentary rock, that was a
coral reef in a tropical sea about 250 million years ago.
In fact, Texas contains mostly sedimentary rocks, with east Texas underlain by a Cretaceous and younger
sequence of sediments. Sedimentary rocks can be found in almost all areas of Texas, save for the High
Plains, which are composed of mostly silts and fine sands, and the Gulf Coastal Plains, which feature mainly
sands and mud. Several of the sedimentary rocks that are abundant in Texas are limestone, lignite, coal,
and gypsum.
A few exposures of Precambrian igneous and metamorphic rocks are found in the central and western parts
of the state, near El Paso. The ancient volcanic (igneous) rocks were formed early in the Earth's history. A
large percentage of the igneous rocks in central Texas is graphite. The metamorphic rocks that characterize
northern and western Texas are largely slate, quartzite, and gneiss.
3 Major Groups of Rocks
Sedimentary
Igneous
Metamorphic
Forms as a result of earth erosion. Small pieces
of earth are worn away (by wind, water, etc.).
They fall into bodies of water and settle to the
bottom. Earth falls upon earth and layers are
formed. Slowly, the bottom layers of earth turn
into rock.
Sedimentary rocks cover 75% of the Earth's
surface.
Forms when molten rock (magma) cools and
solidifies, either below earth’s surface as
intrusive (plutonic) rocks or above the surface as
extrusive (volcanic) rocks.
Over 700 types of igneous rocks have been
described, and most of them are beneath the
Earth's crust.
Forms when a pre-existing rock is transformed
physically and/or chemically by extreme heat
and pressure.
Studying metamorphic rocks provides us with
information about the temperatures and
pressures that occur deep within the Earth's
crust.
Examples:
limestone
sandstone
shale
quartz
magnetite
Examples:
obsidian (volcanic glass)
granite
basalt
granite
andesite
Examples:
slate
quartzite
granulite
phyllite
marble
Quartz
Granite
Marble