Week 4_Three types of rocks_powerpoint presentation
- 1. Lesson 6: Minerals and Rocks
- 2. At the end of the lesson, the learners will be able to: • identify and describe the three basic rock types; • establish relationships between rock types and their mode of origin and environments of deposition/formation; and • understand the different geologic processes involved in rock formation.
- 3. Element Symbol % by wt. of the Earth’s crust % atoms Oxygen O 46.6 62.6 Silicon Si 27.7 21.2 Aluminum Al 8.1 6.5 Iron Fe 5.0 1.0 Calcium Ca 3.6 1.9 Sodium Na 2.8 2.6 Potassium K 2.6 1.4 Magnesium Mg 2.1 1.8 All other elements 1.4 <0.1
- 4. Approximately 85% of the Earth's crust is composed of oxygen and silicon. Together they form the silicon oxygen tetrahedron, which is the basic building block of silicate minerals. Silicates are also termed as (common) rock forming minerals.
- 5. WHAT IS A MINERAL?
- 6. Rocks are an aggregate of minerals. A rock can be composed of a single mineral (e.g. Quartzite is a metamorphic rock composed predominantly of Quartz) or more commonly composed of an aggregate of two or more minerals.
- 7. Can a name of a mineral be also used as a rock name?
- 8. Yes a rock composed predominantly of the mineral Gypsum (CaSO4) is called Gypsum Rock.
- 9. How can we classify rocks? Would it be by color, hardness, texture, density or other physical properties? Is it by chemical composition?
- 10. Generally rocks are classified on the basis of the mode of formation and that some of these physical and chemical properties are inherent on how the rocks are formed.
- 13. - these are rocks that are derived from the cooling and solidification of magma or lava - from solidified molten rock materials, usually hard and crystalline - rate of cooling as one of the most important factors that control crystal size - solidification can occur along the surface of the earth or beneath the surface of the earth
- 14. How is Lava different from Magma? Magma is a molten rock material beneath the surface of the earth. Lava is molten rock material extruded to the surface of the earth through a central vent(volcano) or as fissure eruption.
- 15. Plutonic or intrusive rocks - from solidified magma underneath the earth - gradual lowering of temperature is indicated by the movement of magma from depth to surface causing slow cooling /crystallization -Slow cooling forms large interlocking crystals, a texture called phaneritic. - Examples: granite, diorite, gabbro
- 16. Volcanic or Extrusive rocks - from solidified lava at or near the surface of the earth - fast rate of cooling/crystallization due to huge variance in the temperature between Earth’s surface and underneath common textures: aphanitic, porphyritic, vesicular.
- 17. Volcanic or Extrusive rocks *Common textures: a.) Aphanitic texture: fine-grained texture; minerals not visible to the naked eye; relatively fast rates of cooling/ solidification prevent the formation of large crystals.
- 18. Volcanic or Extrusive rocks *Common textures: b.) Porphyritic texture: formed through two stages of crystallization where in magma partly cooled below the surface of the earth providing time for the large crystals to grow (phenocrysts) before it is extruded to the surface forming the finegrained matrix (groundmass).
- 19. Volcanic or Extrusive rocks *Common textures: c.) Vesicular texture: voids created by rapid cooling which causes air bubbles to be trapped inside.
- 20. Volcanic or Extrusive rocks - examples: rhyolite, andesite, basalt - Pyroclastic rocks: fragmental rocks usually associated with violent or explosive type of eruption. Examples tuff and pyroclastic flow deposits (ignimbrite)
- 21. Igneous rocks are also classified according to silica content and relative amounts of K, Na, Fe, Mg and Ca. They can be classified as felsic, intermediate, mafic and ultramafic, practically based on presence of light and dark colored minerals.
- 22. The relatively dark minerals are olivine, pyroxene, hornblende and biotite. The relatively light colored minerals are plagioclases, Kfeldspars,quartz and muscovite.
- 23. - felsic: granitic: >65% silica, generally light- colored - intermediate: andesitic: 55-65% silica, generally medium colored (medium gray) - mafic: basaltic: 45-55% silica, usually dark colored - ultramafic: <45% silica, generally very dark colored
- 26. - these are rocks that are formed at or near the surface of the Earth - sedimentary processes include: weathering of rocks, erosion, sediment transport and deposition (compaction and cementation)
- 27. • Temperature and pressure at the Earth’s surface are low, allowing for the sedimentary processes to happen • Sediments: solid fragments of organic or inorganic materials from weathered and eroded pre-existing rocks and living matters
- 28. - Common sedimentary features: a.)fossil assemblages: remains and traces of plants and animals that are preserved in rocks b.) stratification or layering (strata which is >1cm is called bedding and < 1cm is called lamination): layering is the result of a change in grain size and composition; each layer represents a distinct period of deposition
- 29. - Common sedimentary features: a.)fossil assemblages: remains and traces of plants and animals that are preserved in rocks b.) stratification or layering (strata which is >1cm is called bedding and < 1cm is called lamination): layering is the result of a change in grain size and composition; each layer represents a distinct period of deposition
- 30. Photo of the Kapurpurawan Formation located at the coastal town of Burgos, Ilocos Norte, courtesy of riderako.com. Shows series of sedimentary strata
- 31. Clastic sedimentary rocks - grains, matrix and cement are the components of clastic rocks - clastic rocks are commonly classified based on particle size - clastic rocks with volcanic origin (e.g. pyroclastics) and may have undergone some stages in the sedimentary processes could be classified as sedimentary rock (e.g. Volcanoclastic rocks).
- 32. Clastic sedimentary rocks - the presence of variable grain sizes (including matrix and cement) is indicative of sedimentary differentiation which is actually a function of processes happening in different sedimentary environments.
- 33. 1.) Grains: greater than sand-sized minerals and/or rock fragments. 2.)Matrix: fine-grained (clay to silt sized) minerals. 3.)Cement: minerals precipitated from solution that binds the grains and matrix together
- 35. 1.) Grains: greater than sand-sized minerals and/or rock fragments. 2.)Matrix: fine-grained (clay to silt sized) minerals. 3.)Cement: minerals precipitated from solution that binds the grains and matrix together
- 36. • Rudaceous Rocks: (rudites) >50% clasts diameter >2mm made up of primarily rock fragments • Arenaceous Rocks: (areAnites) >50% sediments diameter between 0.063-2mm can contain high quartz %. • Argillaceous Rocks: (argillites) >50% sediments diameter <0.063mm and made up mainly of clay minerals and quartz grains to a much lesser extent
- 37. Non-clastic sedimentary rocks - evaporation and precipitation from solution or lithification of organic matter - classified as evaporites (halite, gypsum and dolostone), precipitates (limestone) and bioclastics (coal, coquina)
- 38. Non-clastic sedimentary rocks • Evaporites: rocks formed from the evaporation of water leaving the dissolved minerals to crystallize • Precipitates: rocks formed when minerals from a mineral supersaturated waters start to crystallize at the bottom of the solution • B i o c l a s t i c : rock formed from compacted organic matter
- 41. - formed below the surface of the earth through the process of metamorphism with the recrystallization of minerals in rocks due to changes in pressure and temperature conditions
- 42. 2 KINDS OF METAMORPHISM: 1.) CONTACT METAMORPHISM 2.) REGIONAL METAMORPHISM
- 43. 1.) CONTACT METAMORPHISM - heat and reactive fluids as main factors: occurs when a pre-existing rock gets in contact with magma which is the source of heat and magmatic fluids where metamorphic alterations and transformations occur around the contact / metamorphic aureole of the intruding magma and the rock layers.
- 44. 1.) CONTACT METAMORPHISM The aureole occurs on different scales depending on the sizes of the intruding magma and the amount of water in the intruded rocks and the reactive fluids coming from the magma. - creates non-foliated metamorphic rocks - example: hornfels
- 45. 1.) REGIONAL METAMORPHISM - pressure as main factor: occurs in areas that have undergone considerable amount of mechanical deformation and chemical recrystallization during orogenic event which are commonly associated with mountain belts
- 46. 1.) REGIONAL METAMORPHISM - occurs in a regional/large scale - creates foliated metamorphic rocks - examples: schist, gneiss - non-foliated rocks like marble also form through regional metamorphism, where pressure is not intense, far from the main geologic event
- 47. 1.) REGIONAL METAMORPHISM - occurs in a regional/large scale - creates foliated metamorphic rocks - examples: schist, gneiss - non-foliated rocks like marble also form through regional metamorphism, where pressure is not intense, far from the main geologic event
- 48. • Non-foliated rocks: Hornfels (left), a fine- grained rock that forms through contact metamorphism of noncarbonate rocks. Marble (right), a recrystallized rock that forms from the metamorphism of limestone or dolostone • Foliated rocks: Slate, phyllite, schist and gneiss from shale as precursor rock. The stages of transformation are manifestations of increasing metamorphic grade with increasing pressure
Editor's Notes
- #25: • Granite and Rhyolite have the same chemical composition however Granite on le exhibits phaneritic texture and rhyolite on the right has aphanitic and porphyritic textures. • Diorite and Andesite have the same chemical composition but different textures. Diorite (left) is coarse grained (phaneritic) and andesite (right) is fine grained (aphanitic and porphyritic). • Gabbro and Basalt are of the same chemical composition but differ in texture. Gabbro (left) has larger crystals than basalt (right) which has finer crystals.
- #40: Conglomerate (left) relatively large and rounded clasts as compared to the angular clasts of the breccia on the right • Sandstone (left) with visible grains and prominent layering or; claystone (right) with several embedded fossils • Non - clastic sedimentary rocks limestone (left) and coquina (right)