Geology Chapter 5 Minerals of Earth’s Crust 5.1 What is a Mineral?

5.1 What is a Mineral Objectives Define mineral. Compare the two main groups of minerals. Identify the six types of silicate crystalline structures. Describe three common nonsilicate crystalline structures.

Introduction A mineral is a natural, usually inorganic solid that has a characteristic chemical composition, an orderly internal structure, and a characteristic set of physical properties. Pyrite Sun - Illinois

Characteristics of Minerals An item must pass the “four questions” to be considered a mineral. –Is it inorganic? –Does it occur naturally? –Is it a crystalline solid? –Does it have a consistent chemical composition? If the answer is yes to all the above questions, the item is a mineral.

Characteristics of Minerals

Kinds of Minerals More than 3,000 kinds of minerals have been identified. Fewer than 20 minerals are common – they are called the rock forming minerals. Only 10 of the rock forming minerals make up 90% of the Earth’s crust. Based on their chemical composition, minerals can be classified into one of two groups – silicate minerals and nonsilicate minerals.

Kinds of Minerals Silicate minerals contain a combination of silicon and oxygen, and they may contain one or more metals. For example… –quartz is made only from silicon and oxygen –feldspar, the most common silicate contains potassium (potassium feldspar) or sodium or calcium – or both (plagioclase feldspar) –ferromagnesian minerals are rich in iron and magnesium –Feldspar and quartz alone make up 50% of the Earth’s crust

Kinds of Minerals Nonsilicate minerals do not contain silicon and oxygen and make up about 4% of the Earth’s crust. Nonsilicate minerals are divided into six major categories by their chemical composition. –Carbonates – contain carbonate group (CO 3 ) –Halides – Cl or F combined with Na, K, or Ca –Native elements – pure elements –Oxides – contain oxygen, but no silicon –Sulfates – contain sulfate group (SO 4 ) –Sulfides – one or more elements combined with sulfur

Crystalline Structure A crystal is a solid whose atoms, ions, or molecules are arranged in a regular, repeating pattern. The characteristic geometry of a crystal’s internal structure can be seen in large mineral crystals that grow uninhibited. Minerals are commonly made up of masses of microscopic crystals. Beryl Crystal in Quartz - Brazil

Crystalline Structure of Silicate Minerals The silicon-oxygen tetrahedron is the basic unit of the structure of silicate minerals; a silicon ion chemically bonded to and surrounded by four oxygen ions. mages/tetrahedron.jpg

Crystalline Structure of Silicate Minerals Silicon-oxygen tetrahedra combine in a variety of arrangements to form different silicate minerals. –Isolated tetrahedra – do not link with other silicon or oxygen atoms –Ring silicates – form rings by sharing oxygen atoms –Single-chain silicates – form a chain by sharing oxygen atoms –Double-chain silicates – form when two single chains of tetrahedra bond to each other –Sheet silicates – form when each tetrahedron shares three of it s oxygen atoms with other tetrahedra –Framework silicates – form when each tetrahedron is bonded to four other tetrahedra *See Figure 3 pg. 107.

Six Kinds of Silicate Mineral Arrangements

The Crystalline Structure of Nonsilicate Minerals Nonsilicate minerals display a variety of crystal structures including cubes, hexagonal prisms, and irregular masses. The structure of the nonsilicate mineral determines the characteristics of that mineral. Dogtooth Calcite – Unknown Origin

The Crystalline Structure of Nonsilicate Minerals In native elements, for example, atoms are packed together as close as possible (closest packing). Closest packing results in the higher densities of metals. Each metal atom may be surrounded by 8 to 12 other metal atoms which are as close to each other as the charges of the atomic nuclei will allow. Native Copper - Michigan