THERE ARE THREE TYPES OF ROCKS. THEY ARE: Rocks are made up of one or more minerals. 1. Igneous Rocks: Formed from the cooling of molten rock. A. Extrusive (Volcanic) igneous rocks formed from molten rock that cooled quickly on or near the earth's surface. B.Intrusive (Plutonic) igneous rocks are the result of the slow cooling of molten rock far beneath the surface. 2. Sedimentary Rocks: Formed in layers as the result of moderate pressure on accumulated sediments. 3. Metamorphic Rocks: Formed from older "parent" rock (either igneous or sedimentary) under intense heat and/or pressure at considerable depths beneath the earth's surface.
Igneous Rock Igneous rock forms when magma cools and makes crystals. Magma is a hot liquid made of melted minerals. The minerals can form crystals when they cool. Igneous rock can form underground, where the magma cools slowly. Or, igneous rock can form above ground, where the magma cools quickly.
Kinds of Igneous Rocks Intrusive (plutonic) – formed when magma that crystallized at some depth. Extrusive (volcanic and pyroclastic rocks) formed when molten material reached the earth’s surface (LAVA) and crystallize. In general, extrusive rocks have a finer grained texture than intrusive rocks.
Sedimentary rocks Sedimentary rocks form from pre-existing rock particles - igneous, metamorphic or sedimentary. The Parent rock undergoes WEATHERING by chemical and/or physical mechanisms into smaller particles. These particles are TRANSPORTED by ice, air or water to a region of lower energy called a sedimentary basin. DEPOSITION takes place as a result of a lowering of hydraulic energy, organic biochemical activity or chemical changes (e.g., solubility). Once deposited, the sediments are LITHIFIED (turned into rock) through COMPACTION (decrease in rock volume due to weight of overlying sediment) and CEMENTATION (chemical precipitation in pore spaces between grains which "glues" the rock together. The primary mineralogical and textural characteristics of the rock can be modified as the sediments are buried deeper in the earth's crust and undergo an increase in both temperature and pressure. These low pressure, low temperature changes are termed DIAGENESIS
Detrital sedimentary rocks Detrital sedimentary rocks are those for which the material has been transported as solid particles. The particles themselves may have derived from either physical weathering or chemical weathering. The texture of sedimentary rocks is described as "clastic", meaning that they are composed of discrete particles that are compacted and cemented together. An example of a non-clastic texture would be crystalline material.
Chemical sedimentary rocks Chemical sedimentary rocks derive from material that is carried in solution to lakes and seas. If the solute precipitates out of the solution to form chemical sediments, rocks such as limestone can be formed.
Sedimentary rocks include common types such as chalk, limestone, sandstone, clay and shale.
Metamorphic rocks Metamorphic rock is rock that has been altered by heat or by heat and pressure. ‘Metamorphic' means ‘change of form'; heat and pressure can change the forms of many things, for example, a glassmaker uses heat to change a certain kind of sand into glass. Rocks change when mountain-building forces apply a great deal of pressure and heat to them. Rock is changed by heat produced by nearby molten igneous rock, that is, molten rock, or by both heat and pressure produced mainly by movements in the earth's surface which are associated with the formation of mountains.
Rock Cycle The rock cycle is a general model that describes how various geological processes create, modify, and influence rocks . This suggests that the origin of all rocks can be ultimately traced back to the solidification of molten magma. Magma consists of a partially melted mixture of elements and compounds commonly found in rocks. Magma exists just beneath the solid crust of the Earth in an interior zone known as the mantle.
The Rock Cycle
Rock Cycle Liquid (molten) rock material solidifies at depth or at the earth's surface to form IGNEOUS ROCKS. Uplift and exposure of rocks at the Earth's surface destabilizes these mineral structures. The minerals break down into smaller grains which are transported and deposited as sediments. The sediments are lithified (compacted and cemented), and SEDIMENTARY ROCKS are formed. Changes in temperature, pressure, and/or rock or fluid chemistry can allow igneous and sedimentary rocks to change physically or chemically to form METAMORPHIC ROCKS. At higher temperatures, metamorphic (or any other rock type) rocks may be partially melted, and crystallization of this melt will create igneous rocks. Uplift and erosion can expose all rock types at the surface, re-initiating the cycle.