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Mineral Introduction Chapter 3 Minerals • A mineral is a naturally occurring, inorganic solid, with a definite chemical composition and orderly arrangement of atoms! • All minerals are formed by natural processes on or inside Earth, with no input from humans. • Minerals are crystalline solids which menas that they have a definite compositon and structure. • Crystalline menas that the atoms are arragned in a pattern that is repeated over and over again. Crystals • A crystal is a solid in which the atoms are arranged in orderly, repeating patterns. • A crystal system is a group of crystals that have similar atomic arrangements and therefore similar external crystal shapes. • There are six major crystal systems, which classify minerals according to their crystal structures. 1. Monoclinic 2. Triclinic 3. Orthorhombic • 4. Hexagonal • 5. Cubic • 6. Tetragonal Monoclinic Shape Gypsum! Triclinic Talc Hexagonal Calcite Orthorhombic Sulfur Tetragonal Zircon Cubic Crystals • Crystals can form from magma and solutions of salts. • Hot melted rock called magma, cools at or below Earth’s surface. As magma cools its atoms lose energy and begin to combine into compounds. Molecules of the compounds arrange themselves into repeating patterns. -When magma cools slowly, the crystals that form are large. -When magma cools rapidly, the crystals that form will be small, so that you cannot easily see individual crystals. Crystals • Crystals can also form from minerals dissolved in water. • When water evaporates, the ions that are left behind can come together to form crystals. Or, if too much of a substance is dissolved in water, ions can come together and form crystals out of solution. Mineral Groups • 98% of the Earth’s crust is made of only eight elements. • Most of the common rock-forming minerals belong to the silicates group. • Silicates are minerals the contain silicon (Si) and oxygen (o). Silicon and oxygen are the two most abundant elements in the Earth’s crust. • Feldspar and quartz are two common silicates.