Download How do you Interpret Clues in Rocks?

How Do You Interpret Clues in
Rocks?
Have you ever noticed how
rocks come in different colors,
shapes, and sizes? Rocks are
solid materials that make up the
outer layer of Earth. Geologists
(jee·AHL·uh·jists) study the
properties of rocks to tell how the
rocks may have formed.
One way to study a rock is
to look for minerals
(MIN·uhr·uhlz) in the rock.
Minerals are naturally
occurring substances that are
neither plants nor animals.
Minerals are the building
blocks of rocks.
For example, granite is a rock found in many
areas. It is made of several minerals, as shown
below. If you find a rock with these minerals, you
have found granite.
How can you
identify minerals?
Each mineral has
properties you can
use as clues. One
property of minerals
is color. Look again
at the piece of
granite. What is the
color of each mineral
in the granite?
Color is not always a
useful property. A
mineral may come in
several colors. Mica,
for example, can be
silvery or black.
Quartz can be white,
pink, or purple.
What’s more, both
mica and quartz may
be colorless. Two or
more minerals may
have the same color.
You can tell some minerals
by the way light bounces off
them. This property is called
luster. Some minerals are
shiny like a new metal pan or
coin. Other minerals may
look dull, glassy, or even
“greasy.”
Another clue comes from
rubbing a mineral gently but
firmly on a streak plate. You can
often see a streak that’s the
same color as the mineral
surface. However, pyrite is a
yellow mineral. When you rub it
on a streak plate, you see a thin
trail of black powder.
Another clue is how hard
a mineral is. The harder it
is, the less likely it will be
scratched. Test a mineral’s
hardness with three items –
your fingernail, a penny,
and a nail.
Summarize
• Reread the page about why color is one
property you can use to identify a mineral.
• Write a summary of why color is not
always a useful property when identifying
a mineral in one or two sentences.
What are three ways to tell
minerals apart?
• Answer the question…
– With a partner
– In your Learning Notebook