Minerals Earth Science Ch. 2

Minerals Minerals are not the same as rocks. Most rocks are composed of one or more minerals. Minerals are naturally occurring, inorganic solids with a definite chemical composition and structure. Minerals can be identified by specific chemical and physical properties. Minerals are important because of their uses.

Characteristics of Minerals Naturally occurring Made by natural geologic processes Not made by people Inorganic For the most part minerals do not contain any living material Solid At normal earth surface temperatures Cannot be liquid

Definite chemical composition All minerals are chemical compounds made of 2 or more elements A mineral that only contains one element is called a native element Orderly crystal structure The atoms in a mineral are arranged in an orderly and repetitive manner

Most abundant elements The 4 major elements found in earth’s crust: Oxygen (47%) Silicon (28%) Aluminum (8%) Iron (5%)

Major Rock Forming Minerals There are 4 rock forming minerals that make up the majority of the earth’s crust: Quartz Feldspar Calcite Mica

Groups of Minerals Silicates The most abundant group of minerals on earth. All silicates contain the elements Silicon (Si) and Oxygen (O). All silicates are formed by structures called tetrahedrons. 2 of the most common silicates found at earth’s surface are quartz and feldspar. Quartz: used in glass and electronics Feldspar: used in ceramics

The Silicon Oxygen Tetrahedron 4 oxygen atoms surrounding 1 silicon atom

Carbonates Composed of the carbonate compound CO3. Some of the more common carbonates found in our region include calcite and dolomite. Calcite: used in building materials such as concrete and is very easy to identify because it fizzes when exposed to an acid Dolomite: construction materials

Oxides Composed of oxygen and a metal The reason why metals are rarely found in their native (uncombined) state is because they bind so easily with other elements such as oxygen. Some of the more common oxides include hematite and magnetite Hematite: important ore for iron Magnetite: used as an iron ore and is easy to identify because it is magnetic

Processes that form Minerals Cooling of magma at the surface Precipitation which occurs when substances settle out of water and accumulate Changes in temperature and pressure Hydrothermal solutions which are very hot mixtures of water and dissolved substances.

The most abundant mineral groups found near the earth’s surface are the silicates, carbonates, and oxides. Silicates form from cooling of magma at the earth’s surface. Oxides can form in different ways including cooling of magma, precipitation, and heat and pressure. Carbonates form by precipitation of weathered material.

Ore Minerals Pyrite – sulfur, gold, and iron Magnetite – iron Hematite – iron Galena – lead Graphite – carbon Sulfur – sulfur

Properties of Minerals Color Most easily seen but the least useful in identification because even small amounts of different elements can change color. Streak The color of a mineral in its powdered form Determined by rubbing the mineral against unglazed tile Color may change but streak never does. Luster Used to describe how light is reflected from a surface Many terms can be used but the most common are metallic and nonmetallic

Crystal form Hardness Arrangement of atoms There are 6 different crystal systems Hardness Resistance of a mineral to being scratched Mohs hardness scale goes from 1 (softest) to 10 (hardest) As you move up the scale, the mineral is harder to scratch

Cleavage and fracture Density The way that a mineral breaks The arrangement of the atoms in a mineral will determine if it will cleave or fracture Cleavage: the mineral breaks along flat even surfaces Fracture: the mineral breaks along uneven surfaces Density Relationship of mass to volume The formula is used D=m/v Mass can be determined by using a triple beam balance or scale Volume can be determined by using a graduated cylinder

Distinctive properties of minerals Graphite and talc have distinctive feels Metallic minerals are easy to shape Magnetite is magnetic Transparent calcite displays double refraction Sulfur is easily identified by its smell Carbonates fizz when an acid is dropped on them.