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Learn about the characteristics and formation of minerals, including their crystal structure, composition, and various mineral groups. Discover how geologists identify minerals using physical and chemical properties. Explore the uses of minerals, including their role as ores in mining operations.
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Mineral Characteristics • A mineral is a naturally occurring, inorganic solid with a specific chemical composition and a definite crystalline structure. • Naturally occurring means they are formed by natural processes. • All minerals are inorganic, meaning that they aren’t alive and never were alive during any part of their existence.
A crystal is a solid in which the atoms or molecules are arranged in a definite pattern that is repeated over and over again. There are 6 crystal shapes. Definite Crystalline Structure
Earth’s crust is composed of about 3000 minerals. • Only about 30 minerals are common in Earth’s crust.
Minerals Formation Minerals form by four major processes: • Magma hardening • Changes in pressure • Changes in temperature • Formation of hydrothermal solutions
Mineral Groups Silicates • Silicates are minerals that contain silicon and oxygen, and usually one or more other elements. • Silicates make up approximately 96 percent of the minerals found in Earth’s crust. • The most common minerals, feldspar and quartz, are silicates. • Ex: Olivine is Mg2SiO4
Carbonates • Carbonates are minerals composed of one or more metallic elements with the carbonate compound CO3. • Carbonates are the primary minerals found in rocks such as limestone, coquina, and marble. • Ex: Calcite is CaCO3
Oxides • Oxides are compounds of oxygen and a metal. • Hematite (Fe2O3) and magnetite (Fe3O4) are common iron oxides and good sources of iron.
Sulfates and Sulfides • Sulfates such as anhydrite (CaSO4) are composed of elements with the sulfate compound SO4. • Sulfides such as pyrite (FeS2) are compounds of sulfur and one or more elements.
Halides • Halides such as halite (NaCl) are made up of chloride or fluoride along with calcium, sodium, or potassium.
Native elements • A native element such as silver (Ag) or copper (Cu) is made up of one element only.
Mineral Identification • Geologists rely on several simple tests to identify minerals. • These tests are based upon a mineral’s physical and chemical properties.
Mineral Properties • Minerals have certain physical properties that can be used to identify them. -color -luster -hardness -streak -density -crystal shape -breakage -special properties
Color - Color is easy to see but not always reliable because: • Many minerals have same color • Color can change.
Streak Streak is the color of powder scraped off a mineral when it is rubbed against a rough hard surface. You can find streak by rubbing a mineral across a piece of unglazed porcelain tile (a streak plate).
Luster • Luster is the way that a mineral reflects light from its surface. • Metallic is shiny like a metal. • Nonmetallic luster might be described as dull, pearly, waxy, or silky.
Crystal Structure • A mineral may be identified by it’s crystal structure, one of the six previously mentioned.
Hardness • Hardness is a measure of how easily a mineral can be scratched. • We use Moh's hardness scale. We use different tools to find the hardness- fingernail, penny, nail, glass plate and streak plate. Diamond, the hardest, is a10. Talc, the softest, is a 1. • Any mineral with a greater hardness than another mineral will scratch that softer mineral.
Cleavage • Minerals break along planes where atomic bonding is weak. • Cleavage is the ability of a mineral to split relatively easily and evenly along one or more flat planes.
Fracture • Fracture is the ability of minerals to break with rough, or jagged edges.
Density and Specific Gravity • Differences in weight are the result of differences in density, which is defined as mass per unit of volume. • Density is expressed as a ratio of the mass of a substance divided by its volume, or D = M/V.
Density reflects the atomic weight and structure of a mineral. • The most common measure of density used by geologists is specific gravity. • Specific gravity is the ratio of the weight of a substance to the weight of an equal volume of water at 4°C.
Special properties of minerals also can be used for identification purposes. • A type of calcite called Iceland spar causes light to be bent in two directions, a process known as double refraction, when it passes through the mineral. • Magnetite, an iron ore, is naturally magnetic.
Calcite (CaCO3) fizzes when it comes into contact with hydrochloric acid (HCl).
Mineral Uses • Minerals are virtually everywhere. • They are used to make computers, cars, televisions, etc…
Ores • An ore is a mineral that contains a useful substance that can be mined at a profit. • Examples of ores include Hematite, which contains the element iron and bauxite, which contains the element aluminum.
Mines • Ores are removed by underground mining or from large, open-pit mines. • When a mine is excavated, unwanted rock and dirt, known as waste material, are dug up along with ore.
If the cost of separating the waste material becomes higher than the value of the ore itself, then the mineral will no longer be classified as an ore because it would no longer be economical to mine it. • The classification of a mineral as an ore may also change if the supply of or demand for that mineral changes.
Gems • Gems are valuable minerals that are prized for their rarity and beauty. • Gems such as rubies, emeralds, and diamonds are cut, polished, and used for jewelry. • In some cases, the presence of trace elements can make one variety of a mineral more colorful and thus more prized than other varieties of the same mineral.
