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Rocks and Minerals

Rocks and Minerals. Chapter 13 Red pp. 376 - 396. What is a mineral?. Inorganic, solid materials found in nature Inorganic means they are not formed by plants or animals Rocks are usually made of 2 or more minerals. How do minerals form?.

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Rocks and Minerals

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  1. Rocks and Minerals Chapter 13 Red pp. 376 - 396

  2. What is a mineral? • Inorganic, solid materials found in nature • Inorganic means they are not formed by plants or animals • Rocks are usually made of 2 or more minerals.

  3. How do minerals form? • Magma or lava cools and the atoms combine in orderly patterns. • Evaporation – when seawater evaporates the dissolved minerals crystallize. • Precipitation – water can only hold so much dissolved material, the extra separates and falls out as a solid.

  4. Properties of Minerals • Crystals – solid materials that have an orderly, repeating pattern of atoms • Cleavage–minerals that split into pieces with smooth regular panes. • Fracture - minerals that break into pieces with rough, jagged edges. • Hardness – Mohs Scale classifies minerals from 1 (softest) to 10 (hardest).

  5. More Properties of Minerals • Color – the color of a mineral may be a clue, but don’t rely on color exclusvely since some minerals can occur in a wide variety of colors, and some minerals have the same color as another one. • Streak – scrape a mineral across an unglazed, white tile (called a “streak plate”). If it produces a streak of color, it can help in identification.

  6. And even more properties of minerals…. • Luster – describes how light reflects from a mineral’s surface. Metallic, pearly, glassy, dull are ways to describe a mineral. • Fizz – does the mineral bubble when a weak acid is put on it? • Specific gravity – compares the weight of a mineral with the weight of an equal volume of water.

  7. Common Minerals • Most rock forming minerals are silicates, which contain the elements silicon and oxygen. • Other important rock-forming minerals are carbonates, which contains carbon and oxygen. • Halite is common in the mid-west, and gypsum is abundant in many places.

  8. Gems • Gems are minerals that are rare, and can be cut and polished, giving a beautiful appearance. • They must be clear with no blemishes or cracks. • They must also have a beautiful luster or color.

  9. The Making of a Gem • Gems are so rare because they are produced under special conditions. • Heat, pressure, and certain types of volcanic eruptions are needed to bring diamonds to the surface where they can be mined.

  10. Ores • A mineral is called an ore if it contains enough of a useful substance that it can be sold for a profit. • Most of the metals humans use come from ores. • Iron (for steel) comes from hematite • Lead (for batteries) comes from galena • Magnesium (used in vitamins) comes from dolomite

  11. Ore Processing • Smelting - the ore is melted and separated to remove most of the unwanted materials • Refining – the metal is purified • Processing – into the materials we use every day

  12. Igneous Rocks • Produced when melted rock from inside the Earth cools and hardens • Intrusive Igneous Rocks – formed when magma cools underground, it cools slowly and forms large crystals that can be seen easily. • Extrusive Igneous Rocks – formed from lava that cools quickly above ground. No grains to holes to smooth, glassy appearance depending on how quickly the lava cooled.

  13. Sedimentary Rocks • Sediment is made of broken rock, shells, mineral grains, and other materials. • Formed when sediment is dropped or carried by wind, water, ice, gravity or any other method and collects in layers and hardens over millions of years.

  14. 3 Types of Sedimentary Rocks • I. Detrital Rocks - made of grains of minerals or other rocks that have moved and been deposited in layers, then cemented together by other minerals dissolved in water as well as the weight of sediment above them.

  15. More Sedimentary Rocks • II. Chemical Rocks – formed with seawater, loaded with dissolved minerals, evaporates, leaving layers of the minerals behind. • III. Organic Rocks – formed when living matter dies, piles up and then is compressed into rock. This includes chalk, coal and limestone.

  16. Metamorphic Rocks • Formed when existing rocks are heated to great temperatures or squeezed by great pressure. • Metamorphic means “change of form” • Not only do the resulting rocks look different, they may have recrystallized and be chemically changed also.

  17. Types of Metamorphic Rocks • Foliated rocks – have visible layers or long grains of minerals. The minerals had been heated and squeezed in parallel layers, may have bands of different colored minerals. Includes: slate, gneiss, phyllite, schist. • Nonfoliated rocks – no layers or bands, more even in color and usually no visible grains.

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