Earth Science Chapter 3 Minerals and Rocks Minerals

Earth Science Chapter 3 Minerals and Rocks

Minerals • A mineral is a naturally occurring, solid, inorganic substance that has a definite chemical composition and molecular structure. – Naturally occurring means not made artificially – Inorganic means it is not now, nor ever has been alive. • Minerals are classified on the basis of their physical and chemical properties.

Mineral Characteristics • The physical properties of a mineral are due largely to the internal arrangement of atoms. • The six key physical properties that can be seen or easily tested are: color, streak, luster, hardness, and cleavage or fracture.

Mineral Characteristics • Color – Most visible property – Color alone is not a good mineral identifier. • Many minerals exhibit the same color. • Many minerals are found in a variety of colors.

Mineral Characteristics • Streak – The color of a mineral in its powdered form. – Streak is reliable for mineral identification. • Streak may be different from mineral color.

Mineral Characteristics • Luster – The way in which light is reflected from the surface of a mineral. – Minerals with metallic luster shine like polished metals. – Minerals with nonmetallic luster have no metallic shine. • Nonmetallic lusters can be glassy, dull, earthy, etc.

Mineral Characteristics • Metallic lusters • Nonmetallic lusters

Mineral Characteristics • Hardness – A mineral’s resistance to being scratched – The relative hardness of a mineral is determined by comparing it to the hardness of ten “standard” minerals that make up Moh’s Hardness Scale. – Minerals are often compared to the hardness of glass (5. 5).

Mineral Characteristics • Cleavage – The tendency of a mineral to split along one or more smooth surfaces or planes. Mica (1 plane) Halite (3 planes)

Mineral Characteristics • Fracture – Minerals that don’t show cleavage, fracture unevenly when they break.

Mineral Characteristics • Other properties Magnetic Salty Taste React with Acid Bad Odor

Formation of Minerals • All minerals are crystalline, or made up of atoms arranged in a pattern. • Minerals are grouped according to their chemical composition. – All minerals are made up of elements. – Minerals are classified based upon the elements they contain. – Most common minerals in the crust are silicates (made of silicon and oxygen).

Formation of Minerals – Of all the minerals on the Earth’s crust, over 90% are a combination of the following eight elements: Percent By Mass in Crust

Rocks • Most rocks are composed of one or more minerals. – Rocks composed of one mineral are called monominerallic. – Rocks composed of more than one mineral are called polyminerallic. • Most rocks have a number of minerals in common. – Of the over 2, 500 different minerals, only 10 to 15 minerals compose 90% of rocks.

Rocks • Differences between rocks and minerals – Minerals have a uniform composition while the physical properties of rocks vary from one rock to the next. – Minerals are classified by physical properties while rocks are classified by their origin. • Igneous - solidification of molten rock • Sedimentary - compaction and cementation of sediments • Metamorphic - recrystalization of rock

Igneous Rocks • Igneous rocks form as a result of the solidification of molten rock material. – Molten rock beneath the Earth’s surface is called magma. – Molten rock that reaches the Earth’s surface is called lava. • When molten rock solidifies, it crystallizes into igneous rock.

Igneous Rocks • The texture, or grain appearance, depends on the size and arrangement of crystals. – Intrusive igneous rocks: • Form from magma underground • Solidify slow & have large crystals – Extrusive igneous rocks: • Form from lava above ground • Solidify quick & have small crystals

Igneous Rocks • Igneous rocks are grouped according to their mineral composition. – Felsic igneous rocks • Light color • Low density • Most common on continents – Mafic igneous rocks • Dark color • High density • Most common on ocean floor

Sedimentary Rocks • Sedimentary rocks form as a result of compaction and cementation of sediments. – Sediments are changed into rock after they are transported and deposited. – Most sedimentary rocks are deposited in large bodies of water. – The presence of sedimentary rocks suggests area was underwater at time of formation.

Sedimentary Rocks • Compaction – Pressure created by water and overlying sediments can force particles of sediment close together and compress them into rock. • Cementation – The addition of minerals, such as silica, lime, or iron oxide, tends to glue rock particles together to form solid rock.

Sedimentary Rocks • Clastic Sedimentary Rock – Formed from sediments made up of rock fragments held together by cement – Layers or cementing material are often visible

Sedimentary Rocks • Chemical or Crystalline Sedimentary Rocks – Form as a result of chemical processes • Water with dissolved minerals evaporates • Minerals that precipitate out forms crystals Rock Salt Rock Gypsum

Sedimentary Rocks • Bioclastic or Organic Sedimentary Rocks – Form from remains of dead organisms. • Coal forms as a result of compression of plant remains. • Limestone can be made of shells. Coal Limestone

Metamorphic Rocks • Metamorphic rocks form as a result of recrystallization of unmelted material under conditions of high temperature and pressure over long periods of time. – Recrystallization is a process in which rocks undergo change without true melting. – As a result of heat and pressure minerals in the rocks combine to form new, larger, denser crystalline structures.

Metamorphic Rocks • Banding and foliation of minerals are the most outstanding characteristic of metamorphic rocks. – Due to concentrations of various minerals into zones of different colors – Not to be confused with layering of sedimentary rocks

Metamorphic Rocks • Types of Metamorphism – Contact metamorphism • Molten rock comes in contact with nearby rock • Heat from magma alters the rock it touches – Regional metamorphism • Large areas of rock are under intense heat and pressure • Generally associated with mountain building

The Rock Cycle • The rock cycle describes how rocks of all types can be changed into other rocks. – Earliest rocks formed on Earth were igneous – They were uplifted, weathered, and eroded to form sediments. – The sediments were deposited, buried and compacted into sedimentary rocks. – Sedimentary and igneous rocks were subject to heat and pressure to form metamorphic rocks.

Mineral Conservation • Today the world’s need for energy resources is greater than ever. – Most energy sources-coal, oil, and natural gas -are nonrenewable (used faster than they can be replaced). – Coal oil and natural gas are called fossil fuels because they are made of the remains of plants and animals that lived long ago. – Fossil fuels and other nonrenewable resources are vital to our everyday lives.

Mineral Conservation – Alternate sources of renewable energy resources are under development. • Water power • Wind power • Solar energy • Geothermal energy – The use and distribution of mineral resources have global, financial and political implications. – THEY MUST BE USED WISELY.