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 What is a rock?  ◦ Common rocks: rock is a mixture of minerals, rock fragments, volcanic glass, organic matter and other natural materials.

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Presentation on theme: " What is a rock?  ◦ Common rocks: rock is a mixture of minerals, rock fragments, volcanic glass, organic matter and other natural materials."— Presentation transcript:


2  What is a rock?  ◦ Common rocks: rock is a mixture of minerals, rock fragments, volcanic glass, organic matter and other natural materials

3  Rock cycle illustrates the processes that create and change rocks  Rock interchange between igneous, sedimentary and metamorphic rock depending how they form, the process it takes to form new rock and may take millions of years to form  When matter weathers it is not lost but arranged in perhaps different forms

4  Formation of Igneous Rock: Hot magma cools and solidifies to form igneous rock  Magma: the decay of radioactive elements deep in earth interior and intense pressure cause rocks below 150 km to melt. That melted rock is called magma  Magma is less dense and rises to surface. When it reaches the surface it is called lava

5  Rock that cools underneath the surface is intrusive rock  Cooling is slower and slower than rock that reaches the surface  The slower rock cools the larger the crystal form (coarse grained)

6  Magma cools at the surface and is called extrusive rock  Crystals do not have time to form generally (fine grained)

7  Pumice, obsidian and scoria are examples of volcanic glass  These cool so fast that few or no mineral grains form  Gas is trapped in mineral leading to pockets of gas trapped in mineral

8  Basaltic Rock: rock rich in iron, dark, dense, poor in silica(SiO 2 ) (basalt is an example)  Granitic rock; rich in silica, light colored, lower density: builds up pressure before released. Usually cools before it reaches the surface (granite is example)  Andesitic Rock: composition between basaltic and granitic rock (Cascade Mt are example)

9  Metamorphic rock is changed rock caused by intense pressure and temperature deep under earths surface  Can form from a parent material of igneous or sedimentary rock or metamorphic rock  Shale can change to slate  Slate into schist, and eventually to gneiss

10  Foliated rocks: when mineral grains line up in parallel layers, it is said to have metamorphic foliated texture ◦ Slate: watertight metamorphic rock caused by pressure is used in pools and roofs ◦ Gneiss: forms when granite is put under intense pressure and give layers of light and dark areas

11  Metamorphic rock where layering doesn’t form but form rearrange layers are nonfoliated rocks  Sandstone is sedimentary rock that when heated and under lots of pressure form quartzite with interlocking quartz in between  Marble: composed of mineral calcite (limestone), that has under gone intense pressure and temperature

12  Formation of Sedimentary Rock ◦ 75 % of rocks exposed at the surface are sedimentary rocks ◦ Sediments are loose materials ie rock fragments, minerals grains, bits of shell moved by wind water, ice, or gravity ◦ Sedimentary rocks forms when sediments are pressed and cemented together or when minerals form from solution

13  Rocks that are deposited in layers usually hold the rocks at the bottom of layers are older and younger rocks rest on top  On occasions, the layers get messed up and the age of the rocks don’t hold true to the layers

14  Classified by being either detrital, chemical or organic  Detrital: sedimentary rock made from the broken fragments of other rock which are compacted and cemented together  Rock first must be broken down or weathered and then moved to another location by erosion  Compaction of smaller particles can stick together to form solid rock under pressure

15  Cementation: larger sediment (pebbles and sand) with only pressure can’t bind together, but rather need cementation to hold rock together  Water mixed with dissolved material acts as a cement to hold larger particles together  Shape and size of sediment are given names  Conglomerate (rounded pieces of pebbles cemented together  Breccia are sharp jagged pieces cemented together

16  Can be chunks of minerals, (quartz,feldspar) pieces of gneiss, granite, limestone ◦ The cement usually made up of quartz or calcite  Sandstone is formed from smaller particles  Sand size particles usually quartz and feldspar  Siltstone: similar to sandstone except granules are smaller  Shale: particles made from clay sized particles

17  These rocks are not made from pre-existing rock  These rocks form when dissolved minerals come out of solution  When evaporation takes place in a solution of minerals, they will drop out of solution  Gypsum: rock from New Mexico  Limestone: Calcium carbonate carried to ocean in solution and comes out of solution in form of calcite (usually deposited in shallow lakes)

18  Rock salt: halite forms from salt (NaCl) that evaporates out of solution and forms cubic crystals

19  Rock forms from the once living remains  Most common is fossil-rich limestone  Formed from once living ocean organisms instead of just calcite deposits  Shells of marine organism are made of CaCO 3  that eventually becomes calcite where they are cemented together  Coquina : rock made of shell fragments

20  Chalk: calcite-shell remains of once living ocean organisms  Coal: dead plants are buried under other sediment in swamps  Plants become chemical changed by organisms  United States has a lot of coal produced in Carboniferous period (290-360 million ya)

21  Rock cycle has no beginning or end  Rocks formed can be uplifted, weathered, eroded, buried, cemented, melted, more pressure, uplift continuously

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