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Earth Materials. Rocks and Minerals. Minerals. inorganic solids chemical composition compounds atoms joined together individual elements ex. gold (Au), sulphur (S) two or more elements ex. halite (NaCl). Periodic Table of the Elements. Minerals, cont.
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Earth Materials Rocks and Minerals
Minerals • inorganic solids • chemical composition • compounds • atoms joined together • individual elements • ex. gold (Au), sulphur (S) • two or more elements • ex. halite (NaCl)
Minerals, cont. • Most of the common minerals are made of crystals • What cause that crystalline characteristic? • regular arrangement of the compounds.
Mineral Properties • useful for identification • color • some mineral types occur in many colors • streak: color of mineral powder
Mineral Properties, cont. • luster • metallic vs. nonmetallic • hardness • ability or resistance to scratching • Moh scale (1 to 10) • 1 is softest; 10 is hardest • In 1822 a German scientist by the name of Frederick Mohs set up a scale to determine the approximate hardness of minerals.
Mineral Properties, cont. • cleavage • whether or not mineral split or crack along parallel or flat planes • These planes along which the mineral breaks are called cleavage planes. • If the mineral splits easily along these planes the mineral is then said to have perfect cleavage . • Mica is a good example of perfect cleavage. • Quartz shatters likes glass when struck with a hammer – No cleavage
Mineral Properties, cont. • density • weight per unit volume • crystalline patterns • miscellaneous properties • ex. talc has a distinctive feel
Mineral Types • Silicates • contains mainly compounds of silicon and oxygen • may also contain metallic elements such as iron or magnesium • 75% of Earth’s minerals quartz
Mineral Types, cont. • nonsilicates • remaining 25% • variety of types • native elements • ex. Copper: Cu • combination of elements • ex. Carbonates • Calcite: CaCO3 • Dolomite: CaMg(CO3)2
What eight elements make up over 98% of the Earth's crust? Note: They are, in decreasing quantity as you read downward
The Geologic Cycle Figure 11.5
Rocks • Mostly composed of a combination of minerals • ore deposit • large concentration of an individual mineral
Rocks Cycle • The rock cycle represents the alteration of rock-forming minerals above and below the Earth's surface. • three categories of rocks • igneous • sedimentary • Metamorphic • How they transform?
Igneous RocksFrom Latin word : “ignis” or fire • Forms from the cooling and crystallization of magma or lava • Two main classification schemes: a) texture b) chemistry • Classes by texture • Extrusive Igneous rock • Forms at the earth’s surface as lave cools • ex. Basalt (dark, fine grained) - Pumice (full of holes) , Obsidian (glassy)—pg 335 • Intrusive Igneous rock/Plutonic rocks • Forms deep underground where magma cools slowly. • have a coarse, crystalline texture • ex. granite
Classified by Chemical composition • Felsic • Word derived from Feldspar and Silica • High in silica (65% + • Usually light colored • Ex. Rhyolite (extrusive) Granite (intrusive) • Mafic • Word derived from Magnesium and Ferric (iron) • Low silica content (45-55% or so) • Usually dark-colored • Examples: Basalt (extrusive) and Gabbro (intrusive) • In some text : You may find more divisions based on chemical composition: • Intermediate , Ultramafic • Note: Silica is Silicon dioxide (SiO2)
Pluton • Any intrusive igneous rock can be further divided by size and orientation • Batholith • Laccolith • Dike • Sill Figure 11.7
Sedimentary Rocks • derived from preexisting rocks, or from organic materials • The exogenic processes of weathering and erosion generate the material sediments needed to form these rocks. • deposition, compaction, and cementation CATEGORIES: 3 categories • Detrital/ Clastic • ex. conglomerate, sandstone
Sedimentary Rocks, cont. • chemical types • precipitated from water • ex. Rock salt (halite) limestone (calcium carbonate) • biochemical (organic) types • ex. coal
Metamorphic Rocks Rocks altered in their physical and/or chemical composition by intense heat and/or pressure Metamorphism involves the transformation of a pre-existing rock to form new minerals and textures. Preexisting rock Metamorphic Rock plutonic rocks gneiss
Metamorphic Rocks, cont • Pre-existing rock Metamorphic Rock • shale slate
Metamorphic Rocks, cont • Pre-existing rock Metamorphic Rock • slate schist
Metamorphic Rocks, cont • Pre-existing rock Metamorphic Rock • limestone marble
Metamorphic environments & Processes • Metamorphism occur by two processes: • contact metamorphism • a magma intrusion bakes or recrystallizes rock in a localized area) • occurs under low to moderate pressure and low to high temperature conditions • Temperatures -- vary widely from 400-1000°C. Or… (2) regional metamorphism • where large scale deformation occurs from large scale compression or heating in areas.
METAMORPHIC ROCKS TYPES • Meta. rocks broken down into 2 groups: 1. Foliated metamorphic rocks • Usually associated with regional metamorphism Creates rocks with minerals in distinct bands • Most commonly occur at boundary of tectonic plates • directed pressure • flattens and lengthens the rock in the direction of greatest pressure • Examples of foliated meta. rocks = gneiss & slate. • Non-foliated metamorphic rocks • Usually associated with contact • Lack banding of minerals • Largely occurs formed by Burial metamorphism in deep basins • Examples of non-foliated metamorphic rocks are : • marble • quartzite. Quartzite