Minerals of the Earth’s Crust

Fluorescence is the ability that some minerals have to glow under ultraviolet light. The beauty of mineral fluorescence is well represented at the Sterling Hill Mine in Franklin, New Jersey. In this picture taken at the mine, minerals in the rock glow as brightly as if they had been freshly painted by an artist.

Section 1What Is a Mineral?

mineral is a naturally formed, inorganic solid that has a definite crystalline structure

Mineral StructureElementsare pure substances that cannot be broken down into simpler substances by ordinary chemical means. All minerals contain one or more of the 92 naturally occurring elements.

Atoms and CompoundsEach element is made of only one kind of atom.

atom is the smallest part of an element that has all the properties of that element. Like other substances, minerals are made up of atoms of one or more elements.

compound a substance made of two or more elements that have been chemically joined, or bonded.

A mineral that is composed of only one element is called a native element.

Ascorbic Acid

CrystalsSolid, geometric forms of minerals produced by a repeating pattern of atoms or molecules that is present throughout the mineral

Each mineral has a definite crystalline structure.

All minerals can be grouped into crystal classes according to the kinds of crystals they form.

Two Groups of MineralsSilicate MineralsSilicon and oxygen are the two most common elements in the Earth’s crust.

silicate minerals Minerals that contain a combination of silicon and oxygen

Silicate minerals make up more than 90% of the Earth’s crust.

Silicon and oxygen usually combine with other elements, such as aluminum, iron, magnesium, and potassium, to make up silicate minerals.

Mica Schist

Insulation, rockets, high heat materials, NYC bedrock

Feldspar is used as bonding agent along with magnesium oxide, magnesium chloride and other synthetic glue in the manufacture of abrasives, wheels, discs and other shapes.

Feldspar

Nonsilicate Minerals Minerals that do not contain a combination of the elements silicon and oxygen

Some of these minerals are made up of elements such as carbon, oxygen, fluorine, and sulfur.

Calcite

Fluorite

Gypsum

wallboard, cement, plaster of Paris, soil conditioning, a hardening retarder in Portland cement

construction materials, abrasives, agricultural soil treatments, construction aggregates, pigments, pharmaceuticals

Ornamental uses. As flux in the manufacture of steel. In the making of opalescent glass. As enamels for cooking utensils. As hydrofluoric acid. As elements in place of glass in some high performance telescopes and camera lens.

Section 2Identifying Minerals

ColorBesides impurities, other factors can change the appearance of minerals. The mineral pyrite, often called fool’s gold, normally has a golden color. But if pyrite is exposed to air and water for a long period, it can turn brown or black. Because of factors such as impurities, color usually is not the best way to identify a mineral.

LusterThe way a surface reflects light When you say an object is shiny or dull, you are describing its luster.

Minerals have metallic, submetallic, or nonmetallic luster. If a mineral is shiny, it has a metallic luster. If the mineral is dull, its luster is either submetallic or nonmetallic.

Chrome-metallic luster

Dull

StreakThe color of a mineral in powdered form

A mineral’s streak can be found by rubbing the mineral against a piece of unglazed porcelain called a streak plate. The mark left on the streak plate is the streak.

The streak is a thin layer of powdered mineral. The color of a mineral’s streak is not always the same as the color of the mineral sample.

Unlike the surface of a mineral sample, the streak is not affected by air or water. For this reason, using streak is more reliable than using color in identifying a mineral.

Cleavage and FractureCleavage is the tendency of some minerals to break along smooth, flat surfaces.

Fracture is the tendency of some minerals to break unevenly along curved or irregular surfaces.

This sample of quartz shows a curved fracture pattern called conchoidal fracture

HardnessA mineral’s resistance to being scratched To determine the hardness of minerals, scientists use Mohs hardness scale

The greater a mineral’s resistance to being scratched is, the higher the mineral’s rating is.

To identify a mineral by using Mohs scale, try to scratch the surface of a mineral with the edge of one of the 10 reference minerals. If the reference mineral scratches your mineral, the reference mineral is harder than your mineral.

DensityDensity the measure of how much matter is in a given amount of space. density is a ratio of an object’s mass to its volume.

Density is usually measured in grams per cubic centimeter. Because water has a density of 1 g/cm3, it is used as a reference point for other substances.

Specific GravityThe ratio of an object’s density to the density of

The specific gravity of gold, for example, is 19. So, gold has a density of 19 g/cm3. In other words, 1 cm3 of gold contains 19 times as much matter than 1 cm3 of water contains.

Special Properties

Section 3 The Formation, Mining, and Use of Minerals

Minerals form in a variety of environments in the Earth’s crust. Each of these environments has a different set of physical and chemical conditions. Therefore, the environment in which a mineral forms determines the mineral’s properties. Environments in which minerals form may be on or near the Earth’s surface or deep beneath the Earth’s surface.

MiningOrea mineral deposit large enough and pure enough to be mined for profit.

Rocks and minerals are removed from the ground by one of two methods-surface mining or subsurface mining. The method miners choose depends on how close to the surface or how far down in the Earth the mineral is located.

bauxite

Surface MiningWhen mineral deposits are located at or near the surface of the Earth, surface-mining methods are used to remove the minerals. Types of surface mines include open pits, surface coal mines, and quarries.

Open-pit mining is used to remove large, near-surface deposits of economically important minerals such as gold and copper. ore is mined downward, layer by layer, in an open-pit mine.

Explosives are often used to break up the ore. The ore is then loaded into haul trucks and transported from the mine for processing.

In open-pit mines, the ore is mined downward in layers. The stair-step excavation of the walls keeps the sides of the mine from collapsing. Giant haul trucks (inset) are used to transport ore from the mine.

Quarries are open pits that are used to mine building stone, crushed rock, sand, and gravel. Coal that is near the surface is removed by surface coal mining.

Surface coal mining is sometimes known as strip mining because the coal is removed in strips that may be as wide as 50 m and as long as 1 km.

Subsurface MiningSubsurface mining methods are used when mineral deposits are located too deep within the Earth to be surface mined. Subsurface mining often requires that passageways be dug into the Earth to reach the ore. these passageways may be dug horizontally or at an angle. If a mineral deposit extends deep within the Earth, however, a vertical shaft is sunk. This shaft may connect a number of passageways that intersect the ore at different levels.

Responsible MiningMining gives us the minerals we need, but it may also create problems. Mining can destroy or disturb the habitats of plants and animals. Also, the waste products from a mine may get into water sources, which pollutes surface water and groundwater

Mine ReclamationOne way to reduce the potential harmful effects of mining is to return the land to its original state after the mining is completed.

Reclamation The process by which land used for mining is returned to its original state or better Reclamation of mined public and private land has been required by law since the mid-1970s. Another way to reduce the effects of mining is to reduce our need for minerals. We reduce our need for minerals by recycling many of the mineral products that we currently use, such as aluminum.

The Use of Minerals

GemstonesSome nonmetallic minerals, called gemstones, are highly valued for their beauty and rarity rather than for their usefulness.

Color is the most important characteristic of a gemstone. The more attractive the color is, the more valuable the gem is. Gemstones must also be durable. That is, they must be hard enough to be cut and polished.

caratThe mass of a gemstone is expressed. One carat is equal to 200 mg.

The Cullinan diamond, at the center of this scepter, is part of the largest diamond ever found