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

What is a rock?

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

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

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

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)

Magma cools at the surface and is called extrusive rock

Crystals do not have time to form generally (fine grained)

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

Basaltic Rock: rock rich in iron, dark, dense, poor in silica(SiO2) (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)

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

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

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

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

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

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

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

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

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)

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

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 CaCO3

that eventually becomes calcite where they are cemented together

Coquina : rock made of shell fragments

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)

Rock cycle has no beginning or end Rocks formed can be uplifted, weathered,

eroded, buried, cemented, melted, more pressure, uplift continuously