Themes for Today A huge variety of minerals, but relatively few that make up most of the crust Rocks are composed of minerals The rock cycle describes

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Text of Themes for Today A huge variety of minerals, but relatively few that make up most of the crust Rocks...

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  • Themes for Today A huge variety of minerals, but relatively few that make up most of the crust Rocks are composed of minerals The rock cycle describes the origin, transformation, and erosion of the three types of rocks: igneous sedimentary metamorphic
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  • Earth Materials Minerals and Rocks http://jan.ucc.nau.edu/~rcb7/Vishnu41.jpg
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  • Earth Materials Minerals Minerals have many essential uses common minerals like quartz: glass, sandpaper, optics not-so-common like corundum (ruby): nail files, gemstones everything in between Basic units that make up most of Earths materials
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  • Earth Materials Rocks Rocks are solid aggregates of minerals (few exceptions) Rocks also have many uses crushed for aggregate in cement and for roadbeds sawed and polished rocks for buildings, mantle pieces, and counter tops soils are formed by alteration of rocks
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  • Matter and Its Composition Matter is anything that has mass and occupies space exists as solids, liquids, and gases consist of elements and atoms Element is a chemical substance that cannot be chemically decomposed into simpler substances and is composed of tiny particles called atoms Building a rock...
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  • Atoms Atoms are the smallest units of matter that retain the characteristics of the element Atoms have a compact nucleus containing protons particles with a positive electrical charge neutrons electrically neutral particles particles orbiting the nucleus electrons negatively charged particles
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  • Structure of an Atom Dense nucleus of an atom consisting of protons and neutrons Surrounded by a cloud of orbiting electrons
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  • Atoms Atomic number = the number of protons is constant Atomic mass number = number of protons + number of neutrons may vary due to varying numbers of neutrons
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  • Isotopes An element that has varying numbers of neutrons (and different atomic weights) has multiple isotopes Different isotopes of the same element have different atomic mass numbers behave the same chemically Isotopes are important in radiometric dating
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  • Carbon Isotopes Carbon atoms (with 6 protons) have 7 neutrons = Carbon 13 ( 13 C) have 8 neutrons = Carbon 14 ( 14 C) thereby making up three isotopes of carbon. have 6 neutrons = Carbon 12 ( 12 C )
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  • MineralsThe Building Blocks of Rocks A minerals composition is shown by a chemical formula a shorthand way of indicating how many atoms of different kinds it contains Quartz: SiO 2 Ratio: 1: 2 Quartz consists of 1 silicon atom for every 2 oxygen atoms Orthoclase consists of 1 potassium, 1 aluminum, and 3 silicon for every 8 oxygen atoms KAlSi 3 O 8 1: 1: 3: 8
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  • Native Elements A few minerals consist of only one element They are not compounds They are known as native elements Examples: gold formula: Au diamond formula: C
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  • Minerals California Academy of Sciences in San Francisco
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  • Minerals Geological definition of a mineral: naturally occurring crystalline solid crystalline means that minerals have an ordered internal arrangement of their atoms a narrowly defined chemical composition characteristic physical properties such as density hardness color...
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  • Crystalline Solids By definition, minerals are crystalline solids with atoms arranged in a specific 3D framework If given enough room to grow freely, minerals form perfect crystals with planar surfaces, called crystal faces sharp corners straight edges
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  • Narrowly Defined Chemical Composition Some minerals have very specific compositions examples are halite (NaCl) or quartz (SiO 2 ) Others have a range of compositions because one element can substitute for another if the atoms of the two elements have the same electrical charge and are about the same size example: olivine (Mg,Fe) 2 SiO 4 iron and magnesium substitution in any proportion
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  • Mineral Properties Mineral properties are controlled by Chemical composition Crystalline structure Mineral properties are used for mineral identification and include: cleavage fracture hardness specific gravity color streak luster crystal form
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  • How Many Minerals Are There? More than 3500 minerals are known Only about 2 dozen are particularly common Many others are important resources Mineral groups: minerals with the same negatively charged ion or ion group belong to the same mineral group Most minerals in the crust belong to the group called silicates
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  • Silicates Silicates are minerals containing silica Si and O They make up perhaps 95% of Earths crust and account for about 1/3 of all known minerals
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  • Types of Silicates Ferromagnesian silicates contain iron (Fe), magnesium (Mg), or both Nonferromagnesian silicates do not contain iron or magnesium
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  • Ferromagnesian Silicates Common ferromagnesian silicates include: augite, a pyroxene- group mineral hornblende, an amphibole- group mineral biotite mica olivine
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  • Nonferromagnesian Silicates Quartz Potassium feldspar Plagioclase feldspar Muscovite
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  • Other Mineral Groups Carbonates minerals with carbonate ion (CO 3 ) -2 as in calcite (CaCO 3 ), found in limestone and dolomite [CaMg(CO 3 ) 2 ], found in dolostone Other mineral groups are important, but more as resources than as constituents of rocks
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  • Rock-Forming Minerals Most rocks are solid aggregates of one or more minerals Thousands of minerals occur in rocks, but only a few are common: rock-forming minerals Most rock-forming minerals are silicates, carbonates are also important Accessory minerals are present in small amounts largely ignored in classifying rocks
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  • Rock Cycle The rock cycle represents events leading to the origin, destruction, change, and reformation of rocks Rocks belong to 3 major families igneous sedimentary metamorphic The rock cycle shows how these rock families are interrelated and can be derived from one another
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  • Igneous Rocks All igneous rocks cool and crystallize from magma, solidify from lava, or consolidate from pyroclastic materials Magma is molten material below the surface Lava is molten material on the surface Pyroclastic materials are particles such as volcanic ash
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  • Pyroclastic material Lava Igneous Part of the Rock Cycle
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  • Categories of Igneous Rocks Extrusive or volcanic rocks formed at the surface from lava or pyroclastic materials Intrusive or plutonic rocks formed from magma injected into the crust or formed in place in the crust
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  • Igneous Rocks
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  • Igneous Rock Textures Texture is the size, shape and arrangement of crystals, grains and other constituents of a rock Igneous rocks have 4 textures that relate to cooling rate of magma or lava
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  • 4 Cooling-Rate Textures Phaneritic, with visible grains cooled slowly Aphanitic, with grains too small to see without magnification cooled quickly Porphyritic, with larger grains surrounded by a finer- grained groundmass cooled slowly first, then more quickly Glassy, with no grains cooled too quickly for minerals to grow
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  • Igneous Rock Textures Other textures reveal further details of the formation of the rock Vesicular texture, with holes (vesicles) indicates the rock formed as water vapor and other gases became trapped during cooling of lava Pyroclastic or fragmental texture containing fragments, formed by consolidation of volcanic ash or other pyroclastic material
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  • Igneous Rock Textures Rapid cooling Aphanitic texture Slow cooling Phaneritic texture 2-stage cooling Porphyritic texture
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  • Igneous Rock Textures Glassy texture cooling was too rapid for mineral growth Vesicular texture gasses trapped in cooling lava Pyroclastic texture particles fragmented during eruption
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  • Classifying Igneous Rocks Texture and composition are the criteria used to classify most igneous rocks Composition categories are based on silica content felsic (>65% silica) intermediate (53-65% silica) mafic (45-52% silica) More felsic magmas have higher Na, K, Al More mafic magmas have higher Ca, Fe, Mg
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  • Classifying Igneous Rocks
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  • Common Igneous Rocks BasaltGabbro AndesiteDiorite
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  • Common Igneous Rocks Rhyolite Granite
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  • Classifying Igneous Rocks with Special Textures Texture Vesicular Glassy Pyroclastic or Fragmental Composition Pumice Scoria Obsidian Volcanic breccia Tuff/welded tuff MaficFelsic
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  • Igneous Rocks with Special Textures Tuff has pyroclastic texture. Pumice is glassy and extremely vesicular.
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  • Sedimentary Rocks Sedimentary rocks form by the lithification of sediment In the rock cycle, sedime