National Geographic

Figure 4.13 The tetrahedron formed by silicates contains four oxygen ions bonded to a central silicon atom. Chains, sheets, and complex structures form as the tetrahedra bond with other tetrahedra. These structures become the numerous silicate minerals that are present on Earth.

Single silica oxygen tetrahedron

Two tetrahedra bonded

Figure 4.13 The tetrahedron formed by silicates contains four oxygen ions bonded to a central silicon atom. Chains, sheets, and complex structures form as the tetrahedra bond with other tetrahedra. These structures become the numerous silicate minerals that are present on Earth.

Single silica oxygen tetrahedron

Tetrahedra bonded in three or more directions

Single chain Double chain Sheet Three-dimensional structure

rt^Kipt1 ,n MfttJ^ y0 explore more about the bonding behavior of the silica tetrahedron, visitglencoe.com.

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Figure 4.14 The differences in silicate minerals are due to the differences in the arrangement of their silica tetrahedra. Certain types of asbestos consist of weakly bonded double chains of tetrahedra, while mica consists of weakly bonded sheets of tetrahedra.

Figure 4.14 The differences in silicate minerals are due to the differences in the arrangement of their silica tetrahedra. Certain types of asbestos consist of weakly bonded double chains of tetrahedra, while mica consists of weakly bonded sheets of tetrahedra.

Mica

Vocabulary

Science usage v. Common usage Phyllo

Science usage: the sheets of silica tetrahedra

Common usage: sheets of dough used to make pastries and pies

Individual tetrahedron ions are strong. They can bond together to form sheets, chains, and complex three-dimensional structures. The bonds between the atoms help determine several mineral properties, including a mineral's cleavage or fracture. For example, mica, shown in Figure 4.14, is a sheet silicate, also called a phyllo-silicate, where positive potassium or aluminum ions bond the negatively charged sheets of tetrahedra together. Mica separates easily into sheets because the attraction between the tetrahedra and the aluminum or potassium ions is weak. Asbestos, also shown in Figure 4.14, consists of double chains of tetrahedra that are weakly bonded together. This results in the fibrous nature shown in Figure 4.14.

Carbonates Oxygen combines easily with many other elements, and thus forms other mineral groups, such as carbonates. Carbonates are minerals composed of one or more metallic elements and the carbonate ion CO32-. Examples of carbonates are calcite, dolomite, and rhodochrosite. Carbonates are the primary minerals found in rocks such as limestone and marble. Some carbonates have distinctive colorations, such as the colorful varieties of calcite and the pink of rhodochrosite shown in Figure 4.16.

Figure 4.15

Mineral Use Through Time

The value and uses of minerals have changed over time.

The demand for obsidian—a hard volcanic glass used for tools—produces the first known long-distant trade route.

3300-3000 b.c.

Bronze weapons and tools become common in the Near East as large cities and powerful empires arise.

3300-3000 b.c.

Bronze weapons and tools become common in the Near East as large cities and powerful empires arise.

f 800 b.c. Diamond use spreads from India to other parts of the world to be used for cutting, engraving, and in ceremonies.

The demand for obsidian—a hard volcanic glass used for tools—produces the first known long-distant trade route.

f 800 b.c. Diamond use spreads from India to other parts of the world to be used for cutting, engraving, and in ceremonies.

506 b.c. Rome takes over the salt industry at Ostia. The word salary comes from salarium argentums, the salt rations paid to Roman soldiers.

S 1200-1000 b.c. In the Near East, bronze becomes scarce and is replaced by iron in tools and weapons.

S 1200-1000 b.c. In the Near East, bronze becomes scarce and is replaced by iron in tools and weapons.

506 b.c. Rome takes over the salt industry at Ostia. The word salary comes from salarium argentums, the salt rations paid to Roman soldiers.

98 Chapter 4 • Minerals

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Romqn Argentums

Oxides Oxides are compounds of oxygen and a metal. Hematite (Fe2O3) and magnetite (Fe3O4) are common iron oxides and good sources of iron. The mineral uraninite (UO2) is valuable because it is the major source of uranium, which is used to generate nuclear power.

Other groups Other major mineral groups are sulfides, sulfates, halides, and native elements. Sulfides, such as pyrite (FeS2), are compounds of sulfur and one or more elements. Sulfates, such as anhydrite (CaSO4), are composed of elements with the sulfate ion SO42-. Halides, such as halite (NaCl), are made up of chloride or fluoride along with calcium, sodium, or potassium. A native element such as silver (Ag) or copper (Cu), is made up of one element only.

Economic Minerals

Minerals are virtually everywhere. They are used to make computers, cars, televisions, desks, roads, buildings, jewelry, beds, paints, sports equipment, and medicines, in addition to many other things. You can learn about the uses of minerals throughout history by examining Figure 4.15.

<4800-900 Chinese alchemists combine saltpeter with sulfur and carbon to make gunpowder, which is first used for fireworks and later used for weapons.

f 1546 South American silver mines help establish Spain as a global trading power, supplying silver needed for coinage.

2006 There are 242 uranium-fueled nuclear power plants in operation worldwide with a net capacity of 369.566 GW(e).

<4800-900 Chinese alchemists combine saltpeter with sulfur and carbon to make gunpowder, which is first used for fireworks and later used for weapons.

f 1546 South American silver mines help establish Spain as a global trading power, supplying silver needed for coinage.

2006 There are 242 uranium-fueled nuclear power plants in operation worldwide with a net capacity of 369.566 GW(e).

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2000

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1927 The first quartz clock improves timekeeping accuracy. The properties of quartz make it instrumental to the development of radio, radar, and computers.

Interactive Time Line To learn more about these discoveries and others, visit Earth glencoe.com. 5eiaiK^pr>lini a.d. 200-400 Iron farming tools and weapons allow people to migrate across Africa clearing and cultivating land for agricultural settlement and driving out hunter-gatherer societies.

a.d. 200-400 Iron farming tools and weapons allow people to migrate across Africa clearing and cultivating land for agricultural settlement and driving out hunter-gatherer societies.

1927 The first quartz clock improves timekeeping accuracy. The properties of quartz make it instrumental to the development of radio, radar, and computers.

Interactive Time Line To learn more about these discoveries and others, visit Earth glencoe.com. 5eiaiK^pr>lini

(tl)Wally Eberhart/Visuals Unlimited, (tc)Mark A. Schneider/Visuals Unlimited, (bl)Royalty Free/CORBIS, (bc)Sheila Terry/Photo Researchers iOK^'fl MOtl^

Interactive Table To explore Major Mineral Groups more about major mineral groups, _visit glencoe.com._

Interactive Table To explore Major Mineral Groups more about major mineral groups, _visit glencoe.com._

Group

Examples

Economic Use

Silicates

mica (biotite) olivine (Mg2SiO4) quartz (SiO2) vermiculite

furnace windows gem (as peridot) timepieces potting soil additive; swells when wet

Sulfides

pyrite ( FeS2) marcasite (FeS2) galena (PbS) sphalerite (ZnS)

used to make sulfuric acid; often mistaken for gold (fool's gold)

jewelry lead ore zinc ore

Oxides

hematite (Fe2O3) corundum (Al2O3) uraninite (UO2) ilmenite (FeTiO3) chromite (FeCr2O4)

iron ore, red pigment abrasive, gemstone uranium source titanium source; pigment-replaced lead in paint chromium source, plumbing fixtures, auto accessories

Sulfates

gypsum (CaSO4^2H2O) anhydrite (CaSO4)

plaster, drywall; slows drying in cement plaster; name indicates absence of water

Halides

halite (NaCl) fluorite (CaF2) sylvite (KCl)

table salt, stock feed, weed killer, food preparation and preservative steel manufacturing, enameling cookware fertilizer

Carbonates

calcite (CaCO3) dolomite (CaMg(CO3)2)

Portland cement, lime, cave deposits

Portland cement, lime; source of calcium in vitamin supplements

Native elements

gold (Au) copper (Cu) silver (Ag) sulfur (S) graphite (C)

monetary standard, jewelry coinage, electrical wiring, jewelry coinage, jewelry, photography sulfa drugs and chemicals; distinct yellow color and odor, burns easily pencil lead, dry lubricant

Figure 4.17 Parts of this athlete's wheelchair are made of titanium. Its lightweight and extreme strength makes it an ideal metal to use.

100 Chapter 4 • Minerals

Ric Feld/AP Images llf!? Ores Many of the items just mentioned are made from ores. A mineral is an ore if it contains a useful substance that can be mined at a profit. Hematite, for instance, is an ore that contains the element iron. Consider your classroom. If any items are made of iron, their original source might have been the mineral hematite. If there are items in the room made of aluminum, their original source was the ore bauxite. A common use of the metal titanium, obtained from the mineral ilmenite, is shown in Figure 4.17. Table 4.4 summarizes the mineral groups and their major uses. ^

The classification of a mineral as an ore can also change if the supply of or demand for that mineral changes. Consider a mineral that is used to make computers. Engineers might develop a more efficient design or a less costly alternative material. In either of these cases, the mineral would no longer be used in computers. Demand for the mineral would drop substantially, and the mineral would no longer be considered an ore.

Mines Ores that are located deep within Earth's crust are removed by underground mining. Ores that are near Earth's surface are obtained from large, open-pit mines. When a mine is excavated, unwanted rock and dirt, known as gangue, are dug up along with the valuable ore. The overburden must be separated from the ore before the ore can be used. Removing the overburden can be expensive and, in some cases, harmful to the environment, as you will learn in Chapters 24 and 26. If the cost of removing the overburden becomes higher than the value of the ore itself, the mineral will no longer be classified as an ore. It would no longer be economical to mine.

Gems What makes a ruby more valuable than mica? Rubies are rarer and more visually pleasing than mica. Rubies are thus considered gems. Gems are valuable minerals that are prized for their rarity and beauty. They are very hard and scratch resistant. Gems such as rubies, emeralds, and diamonds are cut, polished, and used for jewelry. Because of their rareness, rubies and emeralds are more valuable than diamonds. Figure 4.18 shows a rough diamond and a polished diamond.

In some cases, the presence of trace elements can make one variety of a mineral more colorful and more prized than other varieties of the same mineral. Amethyst, for instance, is the gem form of quartz. Amethyst contains traces of iron, which gives the gem a purple color. The mineral corundum, which is often used as an abrasive, also occurs as rubies and sapphires. Rubies contain trace amounts of chromium, while sapphires contain trace amounts of cobalt or titanium.

Figure 4.18 The real beauty of gemstones is revealed once they are cut and polished.

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