Minerals and Rocks Properties of Minerals Minerals must : 1.) occur naturally, formed by nature, not by man 2.) form from an inorganic process- from things that were never living 3.) be solid- tightly packed particles 4.) have a crystalline structure-the particles line up in a repeating pattern, flat sides called faces meet at sharp edges and corners. 5.) have a definite chemical combination- only certain elements in definite proportions.
Minerals and Rocks Minerals, Compounds and Elements Almost all minerals are compounds Compound-combination of two or more elements, compound has different properties than either element Different minerals have different combinations of elements quartz-one atom of Si for every two atoms of O (SiO2) Garnet- Si3O12, BUT garnets also contain other elements in set ratios Some elements occur in nature in pure form and not part of a compound ex. Cu, Ag, Au Almost all pure, solid elements are metals
Minerals and Rocks A B Mineral Identification Each mineral has characteristic properties that can be used to identify it Color-both A & B are gold in color, one is the mineral gold, the other is the mineral pyrite (FeS2) Streak-color of minerals powder, streak color and mineral color are often not the same, unlike color, streak never varies for elements that are the same Luster-how light is reflected from a minerals surface; metallic, glassy, earthy (dull), silky, waxy, pearly Copper-metallic Calcite-glassy Kaolinite-dullSerpentine Vein-Silky Chalcedony- waxyBornite-Pearly
Minerals and Rocks Hardness-developed by Friedrich Moh, used to rank hardness of minerals from 1-10 Scratch test done to determine A mineral can scratch any other mineral that is softer than itself, but will be scratched by a mineral that is harder than it fingernail (hardness = 2.5) copper penny (hardness = 3) glass plate or steel knife (hardness = 5.5) steel file (hardness = 6.5)
Minerals and Rocks Density-mass in a given space, mineral size does not matter, density will always be the same for that specific mineral Density of quartz 2.5 g/cm3, diamond 3.5 g/cm3 Density = mass/volume mass is found using triple beam balance volume is found using water displacement in graduated cylinder Crystal Structure-created due to repeating pattern of atoms in mineral All crystals in a mineral have the same structure, used on small minerals Crystals classified based on number of faces (sides) and angles at which the faces meet
Minerals and Rocks Cleavage and Fracture Cleavage- a minerals ability to split easily along flat surfaces Depends on how atoms are arranged, lines up = splitting in one direction Ex. mica Fracture- the way a mineral looks when it breaks apart in an irregular way Most minerals exhibit fracturing Ex. Quartz (curved, shell like surfaces) Special Properties Bending of light to show double images Electrical conductors Glow under UV light Magnetic
Minerals and Rocks How do minerals form Geode-rounded hollow rock that is usually lined with crystals crystals form in geode when water containing dissolved minerals seeps into the cracks or hollow of a rock, then the mineral slowly crystalizes Crystallization-the process where atoms are arranged to form a crystal structure Minerals form three ways 1.) organic processes 2.) from materials dissolved in solutions 3.) as magma and lava cools
Minerals and Rocks Mineral Formation 1. Organic Process All minerals form by inorganic processes, but some form from organic processes as well Ex. ocean animals (clams and corals) produce shells and skeletons made out of calcite 2. Minerals from Solution Elements and compounds that form minerals can be dissolved in water to form solutions solution 1.) Minerals form by evaporation-halite, gypsum, calcite 2.) Minerals from hot water solutions- hot water dissolves elements and compounds and as water cools, crystallization occurs ex quartz, silver, gold, selenite Veins-A narrow deposit of a mineral that is sharply different from the surrounding rock When elements and compounds leave a solution, crystallization occurs
Minerals and Rocks 3. Minerals from magma and lava Hot magma cools inside the crust or as lava hardens on the surface—this causes crystals to form Minerals from magma = quartz, feldspar, tourmaline and mica Minerals from lava = leucite, olivine --magma and lava are rich in oxygen and silicon, otherwise known as silicates silicates make up majority of earth’s crust Size of crystals depend on: 1.) rate that magma cools magma deep in earth cools slowly ---large crystals lava at surface cools quickly—small crystals 2.) amount of gas in magma 3.) chemical composition
Minerals and Rocks Classifying Rocks Geologists study rocks by observing the rocks: 1.) Composition and Color 2.) Texture 3.) Origin Composition and Color Rocks are made of minerals and other mixtures—some have one mineral, others have several Rock-forming minerals-20 minerals that make up Earth’s crust Color provides clues to the mineral composition Granite = light colored rock due to composition-quartz, feldspar, mica, and hornblende (high in silicates), visible grains Basalt = dark-colored, low silica, mineral crystals too small to be seen Like with minerals, color alone cannot be used to identify rocks
Minerals and Rocks Texture Grains-The particles of minerals or other rocks that give rock its texture Texture-the look and feel of a rocks surface Grain Size -Large and easy to see = coarse grain *diorite-igneous -Small, only seen with a microscope = fine grained *slate-metamorphic Grain Shape-due to shape of mineral crystals or other pieces of rock that make up larger rock -rounded (conglomerate-sedimentary) vs. jagged (breccia-sedimentary) Grain Pattern -foliated (banded) = grains in flat layers or swirls of colored bands ex. Gneiss-metamorphic -non foliated (no banding) = no visible patterns ex. Quartzite-metamorphic
Minerals and Rocks Origin Using color, mineral composition, and texture rocks are classified according to their origin Sedimentary-small particles of rocks or the remains of plants and animals are pressed and cemented together --forms in layers buried below the surface CLASTIC Sedimentary Rocks- made up of pieces Grain size smallest to largest- clay, silt, sand Grains larger that 2mm = pebbles Shaleis a rock made mostly of clay, breaks apart in large flat sections. Siltstoneis made up of silt-sized grains Sandstoneis made of sand-sized particles Conglomerateis made of pebbles surrounded by a matrixof sand or mud. BIOLOGICAL Sedimentary Rocks- large numbers of living things die, pile up, and are compressed and cemented to form rock. Coal Limestone -many fossils and is made of calcium carbonate &/or microscopic shells.
Minerals and Rocks Igneous-cooling of magma or lava Intrusive-magma, cools slowly, large, coarse grained texture Extrusive –lava, cools quickly, small grain, fine-grained or even glassy texture, --Hot gas bubbles are often trapped in the quenched lava, forming a bubbly texture Metamorphic- forms when rock is changed due to heat or pressure or by chemical reactions, forms deep under ground Metamorphic rocks are often squished, smeared out, and folded. Metamorphic rocks are the least common of the 3 kinds of rocks. Metamorphic rocks are igneous or sedimentary rocks that have been transformed by great heat or pressure. Despite these uncomfortable conditions, metamorphic rocks do not get hot enough to melt Granite (igneous) Gneiss Shale (sedimentary) Slate Limestone (sedimentary) Marble Sandstone (sedimentary) Quartzite
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Minerals and Rocks Rock cycle- Forces inside Earth and at the surface produce a slow cycle that builds, destroys and changes the rocks in the crust from one kind to another There are many pathways in the rock cycle Here is one example Stone Mountain (Atlanta, GA) made of granite (igneous rock), formed millions of years ago as magma cooled beneath Earth’s surface Mountain building pushed rock to and above surface Weathering and erosion wear away granite forming sand Streams carry sand to ocean Sand piles up and becomes compacted forming sandstone (sedimentary rock) Pressure compacts rock, texture changes from gritty to smooth After millions of years, sandstone changes to quartzite (metamorphic rock)
Minerals and Rocks Plate tectonics drives the rock cycle by forming magma (which forms igneous rock) Where plates move apart-igneous rock formed Where oceanic plate subducts-igneous rock forms (volcano made of igneous rock) Collision of continental plates pushes rock deep, melting forming igneous rock Push up a mountain range, weathering and erosion = sedimentary rock Push rock deep beneath surface, exposing to high heat and pressure = metamorphic rock Conservation of matter Constructive and Destructive Forces build and destroy Earth As rock moves through the rock cycle, material is not lost or gained
Minerals and Rocks The Rock Cycle Through melting, weathering and erosion, and heat and pressure, the rock cycle constantly changes rocks from one type into another type.