Chapter 2 Section 4 How do we identify minerals Objective: Describe the properties that can be used to identify minerals

Key Term physical property: observable characteristic that describes an object streak: color of the powder left by a mineral luster: how a mineral’s surface reflects light hardness: property of a mineral that relates to how much the mineral resists being scratched.

Physical Properties The element iron is gray. Objects made out of iron are attracted to a magnet. These are two physical properties of iron. Physical properties can be used to help identify minerals. Some physical properties of minerals are color, streak, luster, and hardness.

1. LIST What are some physical properties of minerals?

Color and Streak Color is an important property of minerals. However, most minerals cannot be identified by color alone. Many minerals are the same color. Gold and pyrite are both bassy yellow. Other minerals are found in more than one color. Quartz, for example, can be purple, yellow, pink, or colorless. It may also be brown, black, or white. Two minerals that are found only in a single color are malachite and azurite. Malachite is always green. Azurite is always blue.

Color and Streak You can find the streak of a mineral by rubbing the mineral across a square of unglazed ceramic tile. A mineral may be found in many different colors. Its streak, however, is always the same color. Chalk is made up of the mineral calcite. When you write with a piece of naturally occurring chalk, the calcite leaves a white powder that you can see.

2. DESCRIBE: What is the streak of calcite?

Luster A mineral can have either a metallic or a nonmetallic luster. Minerals with a metallic luster shine like new coins. Other minerals may look waxy, glassy, or dull. Quartz has a glassy luster. Calcite has a glassy or a dull luster.

3. IDENTIFY: What are two kinds of luster?

Hardness In 1812, Friedrich Mohs, an Austrian mineralogist, worked out a scale of hardness for minerals. Mohs’ scale ranks ten minerals in hardness from 1 to 10. As the numbers increase, the hardness of the minerals increases. A mineral with a high number can scratch any mineral that has a lower number. However, a mineral with a lower number cannot scratch a mineral that has a higher number?

MOHS’ SCALE OF HARDNESS MineralHardnessMineralHardness Talc1Orthoclase6 Gypsum2Quartz7 Calcite3Topaz8 Fluorite4Corundum9 Apatite5Diamond10

4. ANALYZE: What mineral is hardest on Mohs’ scale?

Classwork CHECKING CONCEPTS 1. What property allows one mineral to scratch another? 2. What is luster? 3. How is the streak of a mineral found?

Classwork THINKING CRITICALLY 4. IDENTIFY: What are some physical properties of the mineral diamond? 5. INFER: Why is streak a better way to identify a mineral than color is?