2. Objectives Classify minerals according to their physical and chemical properties. Identify different types of minerals. Discuss how minerals are used. –luster –streak –hardness –cleavage –fracture –specific gravity –ore –gem Vocabulary Identifying Minerals

3. Mineral Identification Geologists rely on several relatively simple tests to identify minerals. Identifying Minerals These tests are based upon a mineral’s physical and chemical properties. It is usually best to use a combination of tests rather than just one to identify minerals.

4. Mineral Identification Color Identifying Minerals –One of the most noticeable characteristics of a mineral is its color. –Color is sometimes caused by the presence of trace elements or compounds within a mineral. –In general, color is one of the least reliable clues to a mineral’s identity.

5. Mineral Identification Luster Identifying Minerals –Luster is the way that a mineral reflects light from its surface. –Luster is described as being either metallic or nonmetallic. –Metallic luster describes shiny surfaces that reflect light like the chrome trim on cars. –Nonmetallic luster might be described as dull, pearly, waxy, or silky. –Differences in luster are caused by differences in the chemical compositions of minerals.

6. Mineral Identification Texture Identifying Minerals –Texture describes how a mineral feels to the touch. –The texture of a mineral might be described as smooth, rough, ragged, greasy, soapy, or glassy.

7. Mineral Identification Streak Identifying Minerals –Streak is the color of a mineral when it is broken up and powdered. –Sometimes, a mineral’s streak does not match the mineral’s external color. –A mineral’s streak rarely changes, even if it is weathered or its external color varies slightly.

8. Mineral Identification Hardness Identifying Minerals –Hardness is one of the most useful and reliable tests for identifying minerals. –Hardness is a measure of 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.

9. Mineral Identification Hardness Identifying Minerals

10. Mineral Identification Cleavage and Fracture Identifying Minerals –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. –To identify a mineral by cleavage, geologists count the number of cleaved planes and study the angle or angles between them. –Fracture is the ability of minerals to break with arclike, rough, or jagged edges.

11. Mineral Identification Density and Specific Gravity Identifying Minerals –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.

12. Special Properties Special properties of minerals also can be used for identification purposes. Identifying Minerals –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.

13. Mineral Uses Minerals are virtually everywhere. Identifying Minerals They are used to make computers, cars, televisions, desks, roads, buildings, jewelry, beds, paints, sports equipment, and medicines, just to name a few uses.

14. Mineral Uses Ores Identifying Minerals –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.

15. Mineral Uses Mines Identifying Minerals –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.

16. Gems Gems are valuable minerals that are prized for their rarity and beauty. Identifying Minerals 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.

17. Section Assessment 1.Match the following terms with their definitions. ___ streak ___hardness ___ cleavage ___ fracture Identifying Minerals A.the ability to break with arc-like, rough, or jagged edges B.the ability to split relatively easily along one or more flat planes C.the color of a mineral when it is broken up and powdered D.a measure of how easily a mineral can be scratched C D B A

18. Section Assessment 2.How would an oversupply of ore possibly change the mineral’s classification as an ore? Identifying Minerals If an ore is over supplied, it could drive down prices for the ore. This may create a situation in which it would no longer be economical to mine material, thus the material would no longer be classified as an ore.

19. Section Assessment 3.What is specific gravity? Identifying Minerals Specific gravity is the ratio of the weight of a substance to the weight of an equal volume of water at 4ºC. It is a common measure of density used by geologists.