How Do You Interpret Clues in How Do You Interpret Clues in Rocks?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.

SummarizeSummarize

• 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 What are three ways to tell minerals apart?minerals apart?

• Answer the question…– With a partner– In your Learning Notebook