1. 3.3ROCKS

2. What is a Rock? A rock is a naturally occurring solid mixture of one ormore minerals and/or organic material. 3. 3 Different Types of Rocks 4. The Rock Cycle Geologic processes cause rock tochange from one type to another. The rock cycle is the process inwhich rocks are changed by geologicactivity into different types of rocks. Rocks may follow various pathwayswithin the rock cycle. Several variables such astime, heat, pressure, weathering, anderosion may alter a rocks identity. Weathering is a process in which rocks are physically and chemically broken down by water, air, and living things to produce sediment. 5. Bowens Reaction Series In the 1900s, a Canadian geologist namedNorman L. Bowen began studying howminerals crystallize from magma. He learned that as magma cools, certain minerals tend to crystallize first (changes composition of the magma). In 1928, Bowen proposed a simplified patternexplaining the order in which minerals formas magma solidifies, or crystallizes, calledBowens Reaction Series. According to this, minerals form in one of two ways: 1. Continuous formation of plagioclase feldspar:Calcium-Sodium (Ca-Na) rich minerals. 2. Discontinuous formation of Iron-Magnesium(Fe-Mg) rich minerals. 6. Bowens Reaction Series 7. Chemical Stability of Minerals The rate at which a mineral chemically breaks down isdependent on the chemical stability of the mineral. Chemical stability is a measure of the tendency of a chemicalcompound to maintain its original chemical composition ratherthan break down to form a different chemical. Most stable minerals formed at lowest temperatures (similar toEarths surface conditions). Least stable minerals formed at highest temperatures.A fine ceramic is more chemicallystable than a metal when subjectedto HCl. 8. Physical Stability of Minerals Rocks also have natural zones of weakness, determined by howand where the rocks form. Example: Sedimentary rocks may form as a series of layers of sediment. These rocks tend to break between layers. Massive igneous rock structures commonly have unevenly spacedzones of weakness, called joints, that form as the rock cools andcontracts. Below is Devils Postpile National Monument in CA. 9. Igneous Rocks Formation Magma forms when rock melts, when pressure isreleased, or when rock changes composition. Magma is called lava when it is exposed at Earths surface. An igneous rock is a type of rock forming when magma orlava cools and solidifies. 10. Igneous Rocks Formation Minerals with low melting points are the first to melt(composition of the magma changes). The process by which different minerals in rock meltat different temperatures is called partial melting. 11. Igneous Rocks Formation When magma cools, the cooling process is the reverse of partialmelting. Minerals that melted last will crystallize out of the magma first. The crystallization and removal of different minerals from thecooling magma, as occurs in Bowens Reaction Series, is calledfractional crystallization. 12. Igneous Rocks Texture Magma cooling deep insideof Earths crust results inthe formation ofintrusive, orplutonic, igneous rocks. The magma intrudes, orGranitenters, into other rock emasses beneath Earthssurface. The magma thenslowly cools and hardens. Lava cooling at Earthssurface forms extrusive, orvolcanic, igneous rocks.Basalt 13. Igneous Rocks Texture Intrusive igneous rocks commonly have LARGER crystalsbecause they have a slow loss of heat and longer to cool. Igneous rocks composed of large mineral grains aredescribed as having a coarse-grained, or phaneritic, texture. 14. Igneous Rocks Texture Extrusive igneous rocks commonly have smaller crystalsbecause they cool very rapidly. Igneous rocks composed of small mineral grains aredescribed as having a fine-grained, or aphanitic, texture. 15. Igneous Rocks Texture Some igneous rocks can have a mixture of both larger and smaller crystals and their texture is known as porphyritic. The larger crystals (phenocrysts) are surrounded by a background mass of smaller crystals (groundmass). 16. Igneous Rocks Composition Light-colored igneous rocks are called felsic rocks. Large proportions of silica are present along withcommon minerals including quartz, feldspar, and mica.Rhyolite Dark-colored igneous rocks are called mafic rocks. Large proportions of iron and magnesium are presentalong with common minerals includingpyroxene and olivine.Gabbro 17. Igneous Rocks Examples GabbroBasa Rhyolitlt e DioriteAndesiteObsidia Graniten Pumic e 18. Sedimentary Rocks Formation Loose fragments ofrock, minerals, and organicmaterial resulting fromnatural geologic processesare called sediment. Combinations of differenttypes of sediment make upwhat is known assedimentary rocks. The most noticeablefeatures of sedimentaryrock is the layering, orstratification. 19. Sedimentary Rocks Formation Two main processesconvert loose sedimentinto sedimentary rock: Compaction: the processin which sediment issqueezed and the porespace between sedimentgrains is reduced. Cementation: theprocess in whichsediments are gluedtogether by minerals thatare deposited by water. 20. Sedimentary Rocks Classes1. Chemical: forms when the ions from dissolved minerals crystallize, or precipitate, out of a solution. One reason minerals precipitate is due to evaporation (minerals areleft behind once H20 evaporates, thus being called evaporites). Halite is an example of this type of sedimentary rock, made ofsodium chloride, NaCl, or table salt (recall this is also a mineral). The Bonneville Salt Flats near the Great Salt Lake in UT are a goodexample of evaporite deposits. HalitBonneville Salt eFlats 21. Sedimentary Rocks Classes2. Organic: forms from the remains of once-living plants and animals. Most limestone forms from the remains, or fossils, of animalsthat once lived in the oceans. Some are made of the skeletons oftiny organisms called coral (coral reefs). Coal forms from plant remains that are buried before they decayand are then compacted into matter composed mainly of carbon.Fossiliferous CoralBituminousLimestone Reef Coal 22. Sedimentary Rocks Classes3. Clastic: forms when rock or mineral fragments, or clasts, ofpre-existing rocks are compacted or cemented together. Classified by the size of the sediment they contain: Clastic sedimentary rock made of round fragments ranging from 2mm. to boulders is called a conglomerate. If the fragments areangular with sharp corners, the rock is called a breccia. Clastic sedimentary rock made up of sand-sized grains, mainlyconsisting of quartz, is called sandstone. Clastic sedimentary rock consisting of flaky clay-sized particles iscalled shale.ConglomeraBrecciaSandstonShalete e 23. Sedimentary Rocks Features The tendency for currents of air or water to separatesediments according to size is called sorting. 24. Sedimentary Rocks Features The place or setting in which sediment isdeposited is called a depositional environment. Common ones include:RiversBeaches Delta Ocea s ns 25. Sedimentary Rocks Features Some sedimentary rocks are characterized by slanting layers within the rock called cross-beds. Generally form in sand dunes or river beds. 26. Sedimentary Rocks Features A type of stratification (layering) in sedimentary rockwhen different sizes and shapes of sediment settle todifferent levels of rock is called graded bedding. Commonly transition from largest grains on the bottom tosmallest grains on the top. 27. Sedimentary Rocks Features Some sedimentary rocks clearly display ripple marks. Caused by the action of wind or water on sand; often preserved in sandstone and shows the sediment was once part of a beach or river bed. Another feature of sedimentary rocks are mud cracks, which form when muddy deposits dry and shrink. 28. Sedimentary Rocks Examples Brecci aFossiliferouBituminoussCoalConglomera Limestonete Arkos eSandstoneLimestoRedne ShalSandstone e 29. Metamorphic Rocks Formation The process by which heat, pressure, or chemicalprocesses change one type of rock into another is calledmetamorphism. Most metamorphic rock, or rock having undergonemetamorphism, forms deep within Earths crust. 30. Types of Metamorphism1. Contact Metamorphism: a change in the texture, structure, or chemical composition of a rock due to contact with magma. 31. Types of Metamorphism2. Regional Metamorphism: a change in the texture, structure, or chemical composition of a rock due to changes in temperature and pressure over a large area. 32. Metamorphic Rocks Classification Metamorphic rocks are classified according to texture. The metamorphic rock texture in which mineral grains are arranged in planes or bands isGneiss known as foliation. The metamorphic rock texture in which mineral grains are not arranged in planes or bands is called non-foliation.Quartzite 33. Metamorphic Rocks Examples Gnei ssAmphibolite Marble Quartzit eAnthracit e Coal PhyllitSlat eeSchist