Rocks and Minerals posted version

What is a Mineral? Naturally occurring – not man-made Solid - not liquid or gas Inorganic- not part of a living thing Chemical composition-composed of the same type of atoms Crystalline structure-orderly and repeating arrangement of atoms

Minerals Classified by: Chemical composition- what they are made of Crystal structure- how atoms are arranged

Mineral Properties Physical properties are used to identify minerals —Hardness —Cleavage and fracture —Color —Luster —Density —Crystal form

Hardness Resistance of a mineral to scratching Dependent on the strength of a mineral’s chemical bonds. Bond strength is determined by ionic charge, atom (or ion) size, and packing. The Mohs Scale compares the hardness of different minerals.

Cleavage and Fracture Cleavage - breaks along planes of weakness. –Determined by crystal structure and bond strength. Fracture - bond strength is generally the same in all directions. –Minerals that fracture do not exhibit cleavage.

Color Most obvious feature- but it is not reliable for mineral identification.. —A mineral may occur in many color variations or be colorless. —Caused by impurities (trace elements) Luster -How a mineral reflect light (dull, glassy, metallic, etc)

Density Ratio of a mineral’s mass to its volume. In simple terms, it is how heavy a mineral feels for its size (volume).

Mineral Properties: Crystal Form Crystal form (shape)- outward expression of internal arrangement of atoms. Also affected by growth conditions: —Temperature, pressure, space for growth Well-formed minerals are rare in nature—most minerals grow in cramped confined spaces.

Classification of Rock-Forming Minerals Two: —Silicate minerals —Nonsilicate minerals Silicate minerals make up more than 90% of the Earth’s crust.

Nonsilicate Minerals About 8% of Earth’s crust Carbonate minerals (contain CO 3 ) Calcite, dolomite Oxide minerals (metal bonded with 0) Ore minerals—hematite, magnetite, chromite Sulfide minerals (metal bonded with S) Ore minerals—pyrite, galena Sulfate minerals (contain SO 4 ) Gypsum, anhydrate Native elements (only 1 element) Gold, platinum,

The Formation of Minerals and Rock Minerals form by the process of crystallization. Minerals crystallize from: —Magma (molten rock) —Water solutions —Heat and pressure (metamorphism)

Mineral Formation from Cooling Magma Minerals crystallize systematically based on their respective melting points —First minerals - lowest amount of silica and highest melting point —Last minerals - higher amounts of silica and lower melting point

Mineral Formation by Water Hot water solutions from magma account for many important ore deposits As water solutions become chemically saturated, minerals form. Ore deposits can be deposited into cracks or into the matrix of the rock itself.

Water solutions can form chemical sediments such as carbonates and evaporites. This process is called precipitation (forming a solid within a liquid) Mineral Formation by Water

Rock Types The three categories of rock reflect how they were formed: Igneous Cooling and crystallization of magma or lava Sedimentary Pieces (clasts) of rocks that have been glued together Metamorphic Preexisting rock transformed by heat, pressure, or chemical fluids

Igneous Rocks Formed from the cooling and crystallization of magma or lava. —Magma is molten rock that forms inside Earth. —Lava is molten rock (magma) erupted at Earth’s surface.

Generation of Magma Heat: —Temperature increases within Earth’s upper crust—the geothermal gradient—at an average rate of 30°C per kilometer. —Rocks in the lower crust and upper mantle are near their melting points. —Additional heat (rising up from the mantle) induces melting.

Generation of Magma Fluids —Water causes rocks to melt at lower temperatures. Pressure: —Reduced pressure lowers the melting temperature of rock. Example: —The solid inner core

Classification of Igneous Rocks Composition –Percentage of mineral grains present –Silica content of mineral grains Texture –Size of mineral grains Small = fine grained (extrusive) Large = coarse grained (intrusive)

Composition Based on silica content (Silicon and Oxygen) –45-52% - basaltic –52-63% - andesitic –>63% - rhyolitic/granitic

Cooling Rate Depends on location –Underground (plutonic) long time to cool; mineral grains grow large –Above the ground (volcanic) extruded onto the surface, cooling quickly; mineral grains small If a lava cools immediately it forms volcanic glass obsidian- no bubbles pumice or scoria- many bubbles (vesicular)

Volcanoes There are three types of volcanoes: Shield- low, gentle gradient sides Cinder cone- small size, steep sides Composite/stratacone- large, steep sides Each erupts differently.

Composition of lava determines how a volcano erupts –Basaltic (low silica) flows easily & erupts quietly –Andesitic/rhyolitic (high silica) is viscous and traps gas so it erupts explosively

Sedimentary Rocks Sedimentary rocks are products of 4 processes: Weathering Erosion Deposition Sedimentation

Weathering—breaking down the rock Two types: —Mechanical weathering—breaking and disintegration of rocks into smaller pieces (clasts). —Chemical weathering— decomposition, dissolving and transformation of rock into different compounds.

Erosion Physical removal of material Agents-- water, wind, ice, or gravity Does not occur in place - involves movement.

Deposition Deposition — eroded particles come to rest. Larger particles - first Smaller particles are able to remain with the flow. Sediments are sorted according to size as they are deposited.

Sedimentation Deposited horizontally layer by layer. Changes into sedimentary rock by lithification 2 steps: —Compaction —Cementation

Lithification Compaction—Weight of overlying material presses down upon deeper layers. Cementation— “pore water” rich in dissolved minerals acts as a glue to cement sediment particles together.

Classifying Sedimentary Rocks 2 types: —Clastic rocks—transported sediment particles—bits and pieces of weathered rock (shale, sandstone, conglomerate) —Chemical rocks—sediments that were once in dissolved in water. (travertine, halite, limestone)

Clastic Sedimentary Rocks classified by particle size Shale Mud-sized particles, sometimes in thin layers Sandstone Composed of sand-sized particles, quartz common Conglomerates Composed of pebble sized, rounded gravels

Metamorphic Rocks Metamorphic rocks are produced from: —Igneous rocks —Sedimentary rocks —Other metamorphic rocks Metamorphism occurs via recrystallization and mechanical deformation.

Metamorphic Rocks Contact metamorphism: Intruded by magma high temperatures high water content –lots of chemical activity, little mechanical deformation.

Metamorphic Rocks Regional metamorphism: the alteration of rock by both heat and pressure over an entire region Subduction zone- 2 plates coming together.

The Rock Cycle, explained A cycle of formation, change, and destruction Starts with molten rock (magma), which cools and forms igneous rocks… uplift… weathering… erosion…deposition…burial and lithification into sedimentary rocks Then buried … heat, pressure, and fluids, and become metamorphic rocks Eventually, these metamorphic rocks may be heated to the point where they again melt into magma

Shortcuts Doesn't have to work this way: Igneous rocks metamorphose without ever eroding Sedimentary and metamorphic rocks uplift and erode, rather than melting Rocks remain un-eroded and unchanged in stable regions for long periods of time

The Rock Cycle Molten rock rises from the depths of Earth, cools, solidifies, and eventually returns to become magma again.