Rocks  Classified based on their origin (How they formed).  Igneous  Sedimentary  Metamorphic

IGNEOUS  These rocks used to be magma!  Born of fire!  Molten rock (magma) solidifies as it cools allowing crystals to form.  There are two types: Extrusive igneous rock! Intrusive igneous rock!

Extrusive Igneous Rocks (Volcanic)  Form near or at the earth’s surface  Composed of small crystals (Texture)  Not enough time for crystals to grow large!  Rapid crystal growth due to rapid loss of heat!

Intrusive Igneous Rocks (Plutonic) FForm deep under earth’s surface CComposed of Large crystals (Texture) LLots of time for crystals to grow large! SSlow crystal growth due to slow loss of heat!

Naming Igneous Rocks  Use the ESRT  Cross reference (for each sample):  Texture/Grain size  Color  Density  Composition

Distinguishing Characteristics  Look for scattered crystals!  Shiny/glassy looking bits all locked together…  Vesicularity (air pockets)  NOT ARRANGED IN LAYERS

Sedimentary Rocks  These rocks used to be sediments!  Generally form in still water!  There are three types:  Clastic  Chemical (crystalline or evaporites)  Bioclastic

Clastic Sedimentary Rock  Sediments-Small bits of weathered rock are deposited (layed down in layers)  Layers become compressed  Sediment is cemented together by mineral deposits between grains.

Where sediments accumulate: a- alluvial fansj- continental shelf b- Glaciersk-continental slope c- riversl-abyss d- dunesm-reefs e- lakes f- lagoons g- esturies h-deltas i- tidal flats

Chemical/Evaporites  Form as mineral rich water evaporates.  Mineral solidifies as water evaporates and settles out as an evaporite deposit!

Organic/Bioclastic  Form either directly or indirectly from living things.  Coal - Formed as trees and plants decayed over millions of years in swampy areas!!  Limestone - shells and other aquatic wastes combine in layers!

Distinguishing Characteristics  Sedimentary rocks exhibit one or more of these:  Layers of sediments (usually horizontal).  Fossils in the rock!  Earthy (dull) color.  Composed of sediments..NOT crystals!

Naming Sedimentary Rocks  USE THE ESRT  Cross reference your observations with chart on pg.7

Environment of formation inferences!  Large sediments indicate fast water during deposition (shallow, near shore environment).  Small sediments indicate slow water during deposition (deep water environment).  Types of fossils (Land or aquatic environment based on organism).

Metamorphic Rocks (Changed Rocks)  These used to be other rocks!  Formed by heat and/or pressure within the crust!  Rocks re-crystallize without melting!

Types of Metamorphism  Regional – Pressure is the dominant process causing change in rock!  Large areas deep within the earth in areas of mountain building!  Revealed over millions of years by weathering and erosion!

 Contact– Heat is the dominant process causing change!!  Small areas within the crust where magma is injected!  Magma cools but is still hot enough to cause change of the surrounding rock!  MAGMA DOES NOT MELT ROCK

Distinguishing Characteristics  Increased density Pressure squeezes the atoms of the rock closer together…Decreasing the volume without changing the mass!

Foliation  Crystal growth in the direction of pressure…  Causes layers of crystals along which the rock may break…  Much like cleavage in minerals!

Banding  Increased pressures cause new minerals to form with different colors  Appears as alternating dark to light bands around rock!!

Distortion  Twisting of the rock structure due to increased pressure

Rock cycle  Over time ALL rocks can change into any other kind of rock as their environment changes!  Follow the arrows through the Rock Cycle Chart (ESRT).  The process causing change is on the arrow!