Transcript Week Five: Igneous Rock

Week Five: Igneous Rock
Granite, Basalt, Obsidian, Pumice and many others
Igneous Rocks are records of the thermal
history of Earth
Most common of all rocks is Granite:
Granite is a light-colored igneous rock with grains
large enough to be visible with the unaided eye. It
forms from the slow crystallization of magma below
Earth’s surface. Granite is composed mainly of
quartz and feldspar with minor amounts of mica,
amphiboles and other minerals. This mineral
composition usually gives granite a red, pink, gray
or white color with dark mineral grains visible
throughout the rock.
Source: Geology.com
The most common igneous rock in Salt
Lake Valley:
 Quartz Monzonite: Quartz monzonite, a very close relative of, and locally known as
"granite", is a gray, "salt and pepper" igneous rock exposed in the lower reaches of Little
Cottonwood Canyon.
 -Source: Utah Geological Survey
1. Where do igneous rocks occur in your
region and why?
 There are great reserves of granite in Little Cottonwood canyon. Most of the rock is
covered by other type of rock: sedimentary and metamorphic. Since it occurs under a
mountain range, magma collected and then cooled underneath layers of other rock.
2. Did indigenous peoples in your region
use igneous rocks?
 The Ute people are the oldest residents of Colorado, inhabiting the mountains and vast
areas of Colorado, Utah, Wyoming, Eastern Nevada, Northern New Mexico and Arizona.
 Historically, Utes used obsidian rock for every day tools, since this rock is easy to shape and
has sharp edges.
Obsidian is Extrusive Igneous Rock
 Once magma reaches the earth’s surface it is considred lave, colling faster and forming
fine-grained extrusive rock. Utah has large reserves of this fine rock.
3. How are igneous rocks used now?
 Igneous rocks are used for construction, some types for building structures, some types for
pavement. Pumice can also be used as a mild abrasive. Obsidian many times is used for
decorative purposes in decorating and construction.
Uses:
 Granite
 A hard igneous rock consisting of clearly visible crystals of various minerals
 Granite looks attractive when polished and is a very hard rock. It is often used for the
facades (fronts) of buildings, expensive kitchen worktops and gravestones.
Uses:
 Basalt
 A dark-coloured, fine-grained rock. Basalt is one of the main rocks to form the oceanic
crust.
Basalt can be a rich source of iron and is commonly used as an aggregate in the building of
roads.
Uses:
 Pumice
 Pumice is formed in volcanic eruptions when gas is violently released from the still molten
rock creating a rock with thousands of tiny bubbles in it. Pumice’s most obvious trait is that
it is very light, so light in fact that it can sometimes float on water.
 Day to day pumice use revolves around the removal of dead skin from peoples’ feet. It is
also used in abrasive cleaning products and as an ingredient in lightweight construction
materials.
 Source: Mylearning.com
4. Describe two examples of uses of
igneous rocks in your region (if
applicable) or elsewhere.
 In Utah, igneous rocks are used in construction, like construction of our State Capitol
Building, LDS Main Temple, and LDS Administration Building. Native Americans in Utah
region used igneous rock for every day tools, ranging arrowheads and weapons. In some
cases, Obsidian was used and still used for decorative purposes.
Building One: LDS Temple. Location:
Dowtown Salt Lake City.
Rock Type: Quartz: Monzonite from
Little Cottonwood Canyon
Building Two: LDS Adminstrative Building.
Location: Salt Lake City Downtown
Rock Type: Quartz: Monzonite from
Little Cottonwood Canyon
Building Three: Utah Capitol, Main part of
Salt Lake City
Rock Type: Quartz: Monzonite from
Little Cottonwood Canyon