What is a rock? It is a mixture of minerals, organic materials, glasses, and fragments of other rocks. A single-mineral rock is both a rock and a mineral.

3 Rock Categories Based on the method of formation –Igneous –Sedimentary –Metamorphic –As a group they are identified on their composition and texture –For stamps - Which came first?

Igneous Rocks

Lava or Magma?

Igneous Rock Formation Solidification of magma/lava –liquid to solid More specifically – crystallization –Molten lava/magma cools and forms a solid composed of intergrown mineral crystals

Intrusive vs. Extrusive Intrusive = inside –plutonic Extrusive = exit –volcanic

Crystal Size Cause: cooling time –Long cooling time = Large crystals –Short cooling time = Small crystals –Very fast cooling (seconds to hours) = no crystals to very few crystals

Textures of Igneous Rocks Depends on the size of the crystals, the presence of glassy material, & gas pockets (pore space) –Large crystals = coarse-textured rocks –Small crystals = fine-textured rocks –Not visible crystals = glassy –Pore space = vesicular Are fine-textured igneous rocks intrusive or extrusive?

Fine, Coarse, Glassy or Vesicular? 12 34

Identification Based on texture and percent mineral composition

Where it was formed Outside the volcano: Extrusive Inside the Earth: Intrusive

Bubbles? Yes= Vesicular

Bubbles? No=Non-vesicular

Color LightDark Very Dark Neither Light nor Dark Lightest Darkest

Density Light DensityDense Very Dense Medium Density

Finding The Minerals Identify the rock. Unless you have other information, work in the middle of the rock’s box.

This is the amount of Potassium Feldspar in the rock.

This is the amount of Quartz in the rock.

This is the amount of Plagioclase Feldspar in the rock.

Use tick marks on a scrap paper to measure the percentage. Potassium Feldspar 25% Quartz 40%

Practice Name a light-colored, fine-grained rock with no bubbles.

Name a coarse-grained, dense rock.

Name a very light-colored, glassy, extrusive rock with bubbles.

Sedimentary Rock Formed from an accumulation of sediments or organic matteraccumulation –The sediments were weathered or eroded from preexisting rock Most sed. rocks form in water

Cementation Dissolved minerals precipitate out of a solution (i.e. sea water) forming crystalline mineral material –Quartz and calcite

Compaction The weight of the overlying water and/or other sediments compacts sediments This causes a loss of pore space and water

Clastic Sed. Rocks Form from cementation and/or compaction Named based on the size of the sediments

Chemical Sed. Rocks/Evaporites These are the result of evaporation, saturation, or changes in temp. They are composed of crystals of just 1 mineral

Chemical Action Water contains dissolved minerals –i.e. hard water, salt water These minerals precipitate out to form a crystalline mass of intergrown mineral crystals

Organic Processes Any rock made by living organisms or composed of organic material is called a bioclastic sed. rock

Sed. Rock Characteristics Clastic – composed of sediments or clasts Rounded sediments –Water, wind, waves, or currents Sorted sediments –Running water Fossils - Why don’t we find fossils in igneous or metamorphic rocks?

Characteristics Strata – parallel layers of sediments in the rock Surface features –Mud cracks, or ripple marksMud cracks ripple marks Interconnected mineral crystals

Identification

Practice Clastic and splits easily.

Practice Inorganic and has angular fragments.

Practice Microscopic to coarse grains made up of shells.

Practice Chemical and made up of dolomite.

Metamorphic Rock Form due to changes in heat (w/o melting), pressure, and/or mineral fluids Process is called metamorphismmetamorphism Resulting rocks are less porous and more dense

Foliation Layering (aligning) of minerals

Non-Foliated Minerals are random (no alignment)

Recrystallization Process of increasing the size of the mineral crystals or clasts and/or changing the mineral composition (w/o melting) Sandstone to Quartzite

Contact Metamorphism Rocks come in contact with magma or lava The heat and mineral fluids of the liquid rock alter the preexisting rock Usually no foliation due to lack of pressure

Regional Metamorphism Pressure due to colliding plates or from overlying rocks Heat and pressure increase during collisions Highly folded, faulted and foliated rocks

Identification

Practice Fine-grained, foliated rock that contains only mica.

Practice Foliated, banded rock

Practice Non-foliated rock of quartz origin.

Rock Cycle Rock Cycle

Rock Cycle Any rock type can change into any other rock type! No preferred direction of movement. No exact point of separation.

Driving Forces Earth’s interior Sun Gravity

Mudcracks

Ripple Marks