Week 4: Exploring Earth – Igneous Rocks and
Survey the use of rocks used in building
construction in your community. Compare the type of rocks that are used for
building interiors and those that are used for building exteriors. Are any
trends apparent for buildings constructed in the past and those built in more
recent times? If so, are there reasons (cost, shipping, other limitations)
underlying a trend or is it simply a matter of style?
1: Rocks on Earth
Igneous rocksare rocks
that form from the cooling of a hot, molten mass of rock material.Igneous
rocks, as other rocks, are made up of various combinations of minerals. Each
mineral has its own temperature range at which it begins to crystallize,
forming a solid material. Minerals that are rich in iron and magnesium tend to
crystallize at high temperatures. Minerals that are rich in silicon and poor in
iron and magnesium tend to crystallize at lower temperatures. Thus, minerals
rich in iron and magnesium crystallize first in a deep molten mass of rock
material, sinking to the bottom. The minerals that crystallize later will
become progressively richer in silicon as more and more iron and magnesium are
removed from the melt.
rocks that are rich in silicon and poor in iron and magnesium are comparatively
light in density and color. The most common igneous rock of this type is granite,
which makes up most of the earth’s continents. Igneous rocks that are rich in
iron and magnesium are dark in color and have a relatively high density. The
most common example of these dark-colored, more dense rocks is basalt,
which makes up the ocean basins and much of the earth’s interior. Basalt is
also found on theearth’s surface as a result of volcanic activity. Other common igneous rocks are obsidian,
pumice and gabbro that you will investigate through the lab.
this experiment you can chose to either measure 5 different rocks (options
given by your instructor – likely basalt, granite, obsidian, pumice and gabbro)
or 5 different specimen of the same rock.
Decide with your lab partners which you’d like to do.
a balance to find the mass of your first rock. Record the mass in Data Table 4.1.
Tie a 20-cm length of nylon string around the rock so you can lift it with the
string. Test your tying abilities to make sure you can lift the rock by lifting
the string without the rock falling.
an overflow can on a ring stand, adjusted so the overflow spout is directly
over a graduated cylinder.
a finger over the overflow spout, then fill the can with water. Remove your
finger from the spout, allowing the excess water to flow into the cylinder.
Dump this water from the cylinder, then place it back under the overflow spout.
the free end of the string tied around the first rock, then lower the rock
completely beneath the water surface in the overflow can. The volume of water
that flows into the graduated cylinder is the volume of the rock. Remembering
that a volume of 1.0 mL is equivalent to a volume of 1.0 cm3,
record the volume of the rock in cm3
in Data Table 4.1.
6. Calculate the
mass density of this first rock and record the value in the data table.
procedure steps 1 through 5 with 4 more rocks.
1. In what ways
do igneous rocks have different properties?
Explain the theoretical process
or processes responsible for producing the different properties of igneous rock
According to the experimental
evidence of this investigation, propose an explanation for the observation that
the bulk of the earth’s continents are granite, and that basalt is mostly found
in the earth’s interior.
Was the purpose of this lab
accomplished? Why or why not? (Your answer to this question should show
thoughtful analysis and careful, thorough thinking.)
Coordinate systems on Earth
The continuous rotation and revolution of the
earth establish an objective way to determine directions and locations on the
earth. If the earth were an unmoving sphere there would be no side, end, or
point to provide a referent for directions and locations. The earth’s rotation,
however, defines an axis of rotation which serves as a reference point for
determination of directions and locations on the entire surface. The reference
point for a sphere is not as simple as on a flat, two-dimensional surface, because
a sphere does not have a top or side edge. The earth’s axis provides the
north-south reference point. The equator is a big circle around the earth that
is exactly halfway between the two ends, or poles of the rotational axis. An
infinite number of circles are imagined to run around the earth parallel to the
equator. The east- and west-running parallel circles are called parallels.
Each parallel is the same distance between the equator and one of the poles all
the way around the earth. The distance from the equator to a point on a
parallel is called the latitude of that point. Latitude tells you how
far north or south a point is from the equator by telling you on which parallel
the point is located.
Since a parallel is a
circle, a location of 40? N latitude could be anyplace on that circle around
the earth. To identify a location you need another line, one that runs pole to
pole and perpendicular to the parallels. North-south running arcs that
intersect at both poles are called meridians. There is no naturally
occurring, identifiable meridian that can be used as a point of reference such
as the equator serves for parallels, so one is identified as the referent by
international agreement. The reference meridian is the one that passes through
the Greenwich Observatory near London, England, and is called the prime
meridian. The distance from the prime meridian east or west is called the longitude.
The degrees of longitude of a point on a parallel are measured to the east or
to the westfrom the prime meridian up to 180?.
identified with degrees of latitude north or south of the equator and degrees
of longitude east or west of the prime meridian are more precisely identified
by dividing each degree of latitude into subdivisions of 60 minutes (60’) per
degree, and each minute into 60 seconds (60”). In this investigation you will
do a hands-on activity that will help you understand how latitude and longitude
are used to locate places on the earth’s surface.
a lump of clay about the size of your fist. Knead the clay until it is soft and
pliable, then form it into a smooth ball for a model of the Earth.
a sharpened pencil. Hold the clay ball in one hand and use a twisting
motion to force the pencil all the way through the ball of clay. Reform
the clay into a smooth ball as necessary. This pencil represents the
earth’s axis, an imaginary line about which the earth rotates. Hold the
clay ball so the eraser end of the pencil is at the top. The eraser end of
the pencil represents the North Pole and the sharpened end represents the
South Pole. With the North Pole at the top, the earth turns so the part
facing you moves from left to right. Hold the clay ball with the pencil
end at the top and turn the ball like this to visualize the turning Earth.
Earth’s axis provides a north-south reference point. The equator is a
circle around the Earth that is exactly halfway between the two poles. Use
the end of a toothpick to make a line in the clay representing the
- Hold the clay in one hand
with the pencil between two fingers. Carefully remove the pencil from the
clay with a back and forth twisting motion. Reform the clay into a smooth
ball if necessary, being careful not to destroy the equator line. Use a
knife to slowly and carefully cut halfway through the equator. Make a
second cut down through the North Pole to cut away one-fourth of the ball
as shown in Figure 4.1. Set the cut-away section aside for now.