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Minerals 5.2 Composition and Structure of Minerals What is a mineral? • A mineral has the following characteristics: – It occurs naturally. – It is a solid. – It has a definite chemical composition. – Its atoms are arranged in an orderly pattern. – It is inorganic (never alive or produced by something that was alive.) Minerals Name Symbol • There are about 4000 Oxygen O known minerals Silicon Si – Examples) gold, Aluminum Al quartz, halite (salt), diamond Iron Fe • 8 elements make up Calcium Ca 98.5% of the crust’s Sodium Na total mass. Potassium K • Most minerals are Magnesium Mg compounds. Other - % 46.6 27.7 8.1 5.0 3.6 2.8 2.6 2.1 1.5 Minerals Through the Magma Process • Many minerals form out of molten rock. • In magma, atoms or ions can move freely. • As magma cools the atoms, molecules and ions move closer together and form chemical bonds that create compounds. • Many different minerals can form from the same magma mass. • The types of minerals that form depend on: – The types of elements present in the magma – The rate at which the magma cools determines the crystal size. Minerals Through the Pressure Process • When a rock is subjected to high temperature and pressure, the minerals begin to break down chemically. • The temperature and pressure becomes great enough to change the mineral in a solid state. • The free atoms, ions, and molecules recombine forming new minerals. Structure of Minerals • Minerals form crystals. – A regular geometric solid with smooth surfaces called crystal faces. – Contain a regularly, orderly arrangement of atoms. • Although there are thousands of different minerals, there are only 6 basic different shapes of crystals. Six Crystal Systems Silicates • Silicon and oxygen are the two most abundant elements in the Earth’s crust. • Most minerals (90%) contain these two elements and are called silicates. • A silicate may contain one or more metallic elements. • The basic building block of a silicate is the silicate tetrahedron. – Consists of 4 oxygen atoms around a silica atom. – Named for its shape. Silica Tetrahedron