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15 Properties

g ou now know that there are many materials that can be mistaken for i n r e a d Y . Yet diamonds are usually the most expensive. What makes diamonds special? Find out more about diamonds in the reading below.

CHALLENGE What makes diamonds a valuable natural resource?

Materials

For each student 1 completed Student Sheet 13.1, “Data on the Earring Material” 1 Student Sheet 15.1, “Three-Level Reading Guide: Mineral Properties”

Reading Use Student Sheet 15.1, “Three-Level Reading Guide: Mineral Properties” to guide you as you complete the following reading.

Diamonds are such as diamonds, , and are highly valued because they are rare, beautiful, and last a long time. All of these gem- stones are minerals (MIN-er-uls). Minerals are non-living materials that are found naturally on earth. Most minerals are and each one has a particular internal structure, because each one is made of a specific set of atoms that are arranged in a repeating pattern, called a crystalline (KRIS-ta-lin) structure. In the right environment, minerals form large because of their crystalline structure.

Fluorite is a non-living found naturally on earth. It is made of and atoms arranged in a crystalline structure similar to that of diamonds (see Figure 1). For these reasons, fluorite is a mineral. Acrylic and are not minerals. Acrylic is a plastic that is made by people, and glass does not have an internal crystalline structure. The table on the next page lists some common minerals. Which of these minerals do you recognize? Which of these minerals do you use?

B-14 Mineral Properties • Activity 15

Figure 1: Diamonds are made of carbon atoms arranged in the crystalline structure in the diagram at right.This structure results in the octahedral crystal shape of many rough diamonds, shown far right.

Some Common Minerals

Mineral May Also be Called Some Common Uses

corundum rubies, jewelry

fluorite , fluorspar toothpaste, industrial processes

ceramics, electronics, ammunition

halite salt, rock salt table salt, melt snow on roads

native copper, pure copper, wiring, plumbing (past) elemental copper mineral specimens (today)

quartz crystal watches, radios, jewelry

— jewelry, electronics, photography

There are more than 2,000 different minerals, and most of them are not as expensive as diamonds. This is because minerals are found in something that you see everyday: rocks. Rocks are made of minerals. Some of these minerals are very common, while other minerals are harder to find. Large pieces of certain minerals, like diamond, are the hardest to find and are the most valuable. The minerals in most rocks are small, as you can see in Figure 2, below.

Figure 2: Minerals in Rocks Most rocks, like those shown in the photo, are made up of more than one mineral. It is easier to see the different minerals in some rocks than it is in others.

B-15 Activity 15 • Mineral Properties

Identifying Minerals With so many different minerals, it is important to be able to tell one mineral from another. In Activity 13, “Diamond Dilemma,” you made many observations of a mineral. Observations like the ones you made can be used to identify different minerals, and are called properties. Minerals can be classified according to their properties—the characteristics that make them unique.

Color is one property that people sometimes use to identify minerals. Many minerals that are used to make jewelry are known for their beautiful colors. Diamonds are usually colorless, but sometimes they are gray, yellow, or even pink. Because a mineral like a diamond may be found in different colors, color alone cannot be the only property used to identify a mineral.

Some minerals are soft, while others are hard. Hardness is another property used to identify minerals. In 1822, the German scientist Friedrich Mohs created a scale to rank the hardness of a mineral from 1 to 10. He scratched one mineral with another. The mineral that was scratched was softer than the other. Talc, a soft mineral used in talcum powder, has a hardness of 1. Diamond, the hardest mineral on earth, has a hardness of 10. You can see the Mohs Hardness Scale in Figure 3. Today, scientists have created other hardness scales, but the Mohs Scale is still the easiest to use.

On the Mohs Scale, minerals with higher numbers can scratch minerals with lower numbers. Diamonds can be used to scratch any other mineral, but no other mineral—except another diamond—can scratch a diamond. This doesn’t mean that a diamond cannot break. If hit hard enough, a diamond will break into smaller pieces.

There are many other properties that can be used to identify minerals. Geologists (gee-ALL-oh-jists) are people who study rocks, minerals, and other non-living parts of the earth. Geologists also use properties, such as the color a mineral makes when rubbed on a white ceramic plate (called color) and the way a mineral usually breaks (called ), to accurately identify a sample. Since each mineral has a unique set of properties, geologists can tell when a yellow stone is a diamond and not another yellow mineral, like .

B-16 Mineral Properties • Activity 15

Figure 3: Mohs Hardness EVERYDAY MATERIALS MINERALS Scale Compare the hardness of the HARDEST minerals to some everyday 10 Diamond materials. What material(s) could scratch fluorite? What material(s) could scratch corundum? 9 Corundum

8 Topaz

Steel 7 Quartz

6 Orthoclase

Glass

5 Apatite

Platinum 4 Fluorite

3 Native copper Silver Fingernail

2

1 Talc Graphite SOFTEST (pencil lead)

2562 LabAids SEPUP Issues Earth Sci SB B-17 Figure: EaSB B 15.04 (vertical) LegacySansMedium 10/11.5

Note: photos FPO. Activity 15 • Mineral Properties

Finding Minerals Many valuable minerals were formed in the earth over thousands of years. Most of the easy-to-find, valuable minerals have been collected already. To gather minerals today, people usually have to dig into the surface of the earth. They remove large pieces of rock and break them into smaller pieces to find particular minerals. This process is known as . The world’s deepest diamond mine is in South Africa, and it is already over 3.5 kilometers (2.1 miles) deep.

Because not all minerals are found everywhere on earth, people mine for particular minerals in certain parts of the world. For example, diamonds are commonly mined in the countries of Canada, Botswana, South Africa, Russia, and Australia. (See Figure 4.)

Figure 4: Some Countries that Russia Produce Diamonds Canada Countries that produce a lot of diamonds are shown in orange.

Botswana Australia

South Africa

Today, not all minerals are mined from the earth. Some can now be created 2562in laboratories LabAids SEPUP and Issues are called Earth syntheticSci SB (sin-THET-ik). Even though Figure: EaSB B 15.05 LegacySansMediumsynthetic mineral 10/11 substitutes.5 are made by humans, they are not fake. They have the same structure and other properties as the natural mineral. But synthetics are not defined as minerals since they are not found naturally on earth.

B-18 Mineral Properties • Activity 15

Analysis

1. a. Create a concept map using the following 10 words: rocks properties minerals color diamonds hardness fluorite Mohs Hardness Scale geologists crystalline structure

b. Add at least five more words related to minerals to your concept map. Choose words that show what you now know about minerals.

2. What makes diamonds a valuable natural resource?

3. Does the size of a mineral affect its properties?

4. Look at Student Sheet 13.1, “Data on the Earring Material,” from Activity 13, “Diamond Dilemma.” Besides color and hardness, what are some other properties that can be used to identify a mineral?

5. Look at Student Sheet 13.1 again. Compare your observations to the Mohs Hardness Scale. Is the hardness of the earring material most likely to be 1, 4, or 8? Explain your reasoning.

Extension 1 Do you want to see more minerals? Bring in any minerals you may have collected to share with your class or go the Issues and Earth Science page of the SEPUP website to link to sites with photos of valuable gemstones and other minerals.

Extension 2 Minerals like diamonds get their shape when they are formed in the earth when molten rock cools. Minerals that can dissolve in water form crystals as the water evaporates. To try this yourself, dissolve as much salt or epsomite (epsom salts) as you can in some warm water. Pour the solution into a large open jar. Next, tie a piece of string around the middle of a pencil and place the pencil across the mouth of the jar. Let a small length of the string dip into the solution. Keep the jar as still as possible as you allow the water to evaporate (the more water you use, the longer it will take to evaporate). Examine the crystals that form on the string, either with a magnifying or a microscope. Will all of the crystals from a single mineral have the same crystal shape? What is your prediction?

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