MINERALS CHAPTER 4

Minerals play important roles in forming rocks and in shaping Earth’s surface, and a select few have played a role in shaping civilization. WHAT IS A MINERAL? Earth’s crust is composed of about 3000 minerals.

DEFINITIVE MINERAL CHARACTERISTICS ALL MINERALS : – are solids – have a unique chemical composition – majority are made from compounds. – crystalline (Have atoms or molecules that are arranged in regular geometric patterns that are repeated again and again) Naturally Occurring and Inorganic

MINERAL CHARACTERISTICS Definite Crystalline Structure – At times and fairly rare, a mineral will form in an open space and grow into one large crystal, possibly taking the shape of one of the six major crystal systems. Cubic Tetragonal Hexagonal Orthorhombic Monoclinic Triclinic

MINERALS FROM MAGMA Minerals can form from the cooling of magma. Magma is molten material found beneath Earth’s surface. elements present in the magma determine which minerals will form Small crystals form from rapidly cooling magma Large crystals form from slowly cooling magma.

MINERALS CAN FORM FROM SOLUTION water in a solution can dissolve only so much of a solid before the water becomes saturated. – If a solution becomes supersaturated mineral crystals may begin to precipitate (what does this mean?) – If liquid evaporates from a supersaturated (what is this word?) solution, the elements remain behind and may begin to arrange into crystals.

MINERAL GROUPS About 30 minerals are common in Earth’s crust. What is a mineral? most common minerals are often referred to as rock-forming minerals. WHY? The vast majority of minerals are made up of the eight most common elements. What do you think these are?

MINERAL GROUPS Silicates – are minerals that contain silicon and oxygen, and usually one or more other elements. – make up approximately 96 percent of the minerals found in Earth’s crust. – The most common minerals, feldspar and quartz, are silicates. Is this a surprise?

Carbonates – composed of one or more metallic elements with the carbonate compound CO 3. – primary minerals found in rocks such as limestone, coquina, and marble.

MINERAL GROUPS What is a mineral? – Oxides – compounds of oxygen and a metal. – Hematite (Fe 2 O 3 ) and magnetite (Fe 3 O 4 ) are common iron oxides and good sources of iron.

OTHER MINERAL GROUPS – Other major mineral groups are sulfides, sulfates, halides, and native elements. Sulfides such as pyrite (FeS 2 ) are compounds of sulfur and one or more elements. Sulfates such as anhydrite (CaSO 4 ) are composed of elements with the sulfate compound SO 4. 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.

MINERAL IDENTIFICATION several relatively simple tests to identify minerals. based upon a mineral’s physical and chemical properties. usually best to use a combination of tests WHY?

MINERAL IDENTIFICATION Color Identifying Minerals – One of the most noticeable characteristics – sometimes caused by the presence of trace elements or compounds within a mineral. – one of the least reliable clues to a mineral’s identity. – Reliable?

Luster – way that a mineral reflects light from its surface. – either metallic or nonmetallic. – Metallic luster: shiny surfaces that reflect light ex. chrome trim on cars. – Nonmetallic luster: dull, pearly, waxy, or silky. What Causes these differences?

Texture – how a mineral feels to the touch. – smooth, rough, ragged, greasy, soapy, or glassy.

Streak – color of a mineral when it is broken up and powdered. – does not always match the mineral’s external color. – rarely changes, even if it is weathered or its external color varies slightly.

Hardness – one of the most useful and reliable tests for identifying minerals. – how easily a mineral can be scratched. – German geologist Friedrich Mohs developed a scale in which an unknown mineral’s hardness can be compared to the known hardnesses of ten minerals. – Any mineral with a greater hardness than another mineral will scratch that softer mineral.

Cleavage and Fracture – Minerals break along planes where atomic bonding is weak. – Cleavage : split relatively easily and evenly along one or more flat planes. – geologists count the number of cleaved planes and study the angle or angles between them. – Fracture : break with arclike, rough, or jagged edges.

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. – Calcite (CaCO 3 ) fizzes when it comes into contact with hydrochloric acid (HCl). – Magnetite, an iron ore, is naturally magnetic. – The mineral sphalerite produces a distinctive rotten-egg odor when it is rubbed vigorously across a streak plate.

MINERAL USES Ores – 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.

MINERAL USES Identifying Minerals – Ores are removed by underground mining or from large, open-pit mines.. – 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 valuable minerals that are prized for their rarity and beauty. Identifying Minerals rubies, emeralds, and diamonds are cut, polished, and used for jewelry. presence of trace elements can make one variety of a mineral more colorful and thus more prized than other varieties of the same mineral.