Formation of Rocks

1.Rhyolite 1.Rhyolite—fine- grained texture, extrusive formation, SiO 2 and feldspar minerals, granitic composition 2.Obsidian 2.Obsidian—compact glassy texture, extrusive formation, SiO 2 (quartz) 3.Pumice 3.Pumice—frothy glassy texture, extrusive formation, quartz

1.As the rate at which molten rock cools increases, the size of the mineral grains increases. intrusive extrusive 2.You can determine if an igneous rock has had an intrusive (coarse- grained) or extrusive (fine or glassy) origin by its texture. 4.A light colored igneous rock is less dense than a dark colored igneous rock.

lava magma 5.The main difference between lava (on) and magma (beneath) is its location in relation to the Earth’s surface. porphyritic 6.A porphyritic texture is an adjective that describes an igneous rock with appreciable phenocrysts (prominent embedded crystals). Conclusion: Igneous rocks are classified on the basis of texture and composition.

Clastic—Texture 1.Conglomerate 1.Conglomerate—rounded gravel fragments, formed via compaction and cementation 2.Sandstone 2.Sandstone—quartz, compaction and cementation 3.Shale 3.Shale—clay, compaction and cementation Chemical—Composition 4.Fossiliferous Limestone 4.Fossiliferous Limestone— organic calcite (CaCO 3 ), evaporation method of lithification

1.The size range for gravel is over 2 mm. The minimum and maximum dimensions for sand is 1/16 to 2mm. clastic chemically 3.You can distinguish a clastic (grain size) from a chemically (crystalline or shells) formed sedimentary rock by the texture. evaporite 4.The sequence of events in the formation of an evaporite can be described as dissolved substances precipitate, or separate from solution when water evaporates or boils off leaving a solid.

crystalline organic 5.The crystalline texture of a chemical limestone (formed by evaporation) can be distinguished from an organic limestone shelly texture (formed by cementation). lithification 6.The sequence of events in the lithification of sandstone can be described by ordering the processes of weathering, erosion, deposition, compaction, and cementation. Conclusion: Sedimentary rocks are classified by texture, composition, and mode of formation.

Foliated 1.Schist 1.Schist—contact metamorphism, phyllite parent rock 2.Gneiss 2.Gneiss—contact metamorphism, granite origin Nonfoliated 3.Quartzite 3.Quartzite—regional metamorphism, sandstone origin

1.Metamorphic rocks formed by contact metamorphism are usually not dense and resistant because they are changed as a result of being in contact with hot magma. 3.You seldom find fossils in metamorphic rocks because these are fragile imprints of plant and animal remains easily deformed beyond recognition under pressure. 4.Pressure often causes minerals in metamorphic rocks to rearrange in layers.

5.Quartzite tends to be hard and resistant because it is a regional metamorphic rock formed by forces acting over wide areas under extreme conditions. foliated nonfoliated Conclusion: Metamorphic rocks are classified on the basis of texture (foliated or nonfoliated) and composition (parent rock)