Identifying Minerals — Reading Comprehension Lesson

Reading Passage

Identifying Minerals

A mineral is a naturally occurring solid substance found in the earth. Minerals are not alive and are not made by living things. Rocks are made up of one or more minerals, and there are thousands of different minerals found throughout Earth’s crust. Scientists who study minerals are called mineralogists, and they use several physical properties to identify them.

One of the most useful properties for identifying a mineral is its hardness — how resistant it is to being scratched. Scientists use a scale called the Mohs Hardness Scale, which ranks minerals from 1 (the softest) to 10 (the hardest). Talc is the softest mineral on the scale, and diamond is the hardest. A mineral can scratch any other mineral that is softer than itself.

Luster describes how a mineral reflects light from its surface. Some minerals have a metallic luster and shine like a metal. Others have a nonmetallic luster and might appear glassy, waxy, silky, or dull. Gold, pyrite, and galena are examples of minerals with metallic luster. Quartz has a glassy, nonmetallic luster.

Color is another property of minerals, but it can be misleading because many different minerals share the same color. A more reliable test is streak — the color of a mineral’s powder when it is rubbed against a rough white tile called a streak plate. The streak of a mineral is often different from the color of the mineral itself, which makes it a more useful clue.

Cleavage and fracture describe how a mineral breaks. A mineral that breaks along flat, smooth planes is said to have cleavage. Mica, for example, breaks into thin flat sheets. A mineral that breaks with rough or uneven surfaces is said to fracture. Scientists use all of these properties together — hardness, luster, color, streak, cleavage, and fracture — to identify unknown minerals.

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