Earth science Rock cycle, Igneous rocks

6.1 The Rock Cycle Rock- a group of minerals bound together in some way Can consist of one mineral, but usually multiple minerals Rocks form from other rocks This relationship is seen in the rock cycle (p 119)

Types of Rocks 1.Igneous- formed by the cooling and hardening of magma (hot molten rock) 2.Sedimentary- formed by the compaction and cementation of sediment (rock fragments, plant remains& minerals that have settled out of solution) 3.Metamorphic- formed from the effect of heat and pressure on preexisting rocks

6.2 Igneous Rocks Categorized by composition, then texture Texture is caused by cooling environment

Magma/ Rocks with Felsic Composition Thick and slow moving magma Cooler (though still very hot) Large amounts of silica Light colored rocks Violent eruptions- builds up pressure Mt. St. Helens (actually closer to intermediate, but close enough)

Magma/ Rocks with Mafic Composition Thinner, faster moving magma Hotter Large amounts of Fe & Mg, little Si Dark colored rocks (ferromagnesian silicates) Calm eruptions- releases pressure often Hawaii

Textures- Extrusive (aka Volcanic) Cools above the ground, very quickly Small crystals, microscopic crystals or no crystallization (not crystalline is not a mineral, has glassy texture- obsidian) Pumice is created when gas bubbles are “frozen” into quickly cooling rock

Obsidian

Texture: Intrusive (Plutonic) Cools below the surface very slowly Large crystals Other texture: porphyry- cools below ground, then ejected and cools fast- has large crystals surrounded by small ones

Igneous Rock Families By composition, members have differing textures 1.Granite family- felsic, fine grained is rhyolite, coarse is granite 2.Gabbro family- mafic, fine- basalt, coarse is gabbro 3.Diorite family- intermediate, fine- andesite, coarse- diorite 4.Ultramafic

Granite & Rhyolite

Gabbro & Basalt

Diorite & Andesite

Ultramafic- Peridotite

Plutons (taken from 6.2) A rock mass that forms when magma cools inside Earth’s interior 1.Batholith 2.Laccolith 3.Stock 4.Sill 5.Dike

6.3 Sedimentary Rocks 3 main types of sedimentary rocks: 1.Clastic- formed from fragments of other rocks (sediment) 2.Chemical- Form when minerals precipitate (fall out) of solution 3.Organic- Forms from sediments consisting of the remains of plants and animals

Clastic

Chemical

Organic

Clastic Sedimentary Rocks Sediment size (large to small): Boulder, Cobble, Pebbles, Gravel, Sand, Silt, Clay Eroded and deposited by running water Larger sizes are first to be deposited, near shore, smaller particles such as sand, silt and clay are deposited further off shore (p 127) Once sediment is deposited it must be cemented

Boulders

Pebbles

Sand

Cementation Once sediment is deposited it must be cemented Cementation- the binding of loose sediment by minerals filling the space between grains Silica (SiO2), Calcite (CaCO3) and Iron oxide/ hematite can act as cements

Cement

Clastic Sedimentary Rocks 1. Conglomerate- rounded coarse sand and pebbles are cemented together 2.Breccia- similar to conglomerate, but particles are angular 3.Sandstone- sand is cemented 4.Shale- made of clay- often breaks in sheets

Conglomerate

Breccia

Sandstone

Shale

Chemical Sedimentary Rocks 1.Rock salt- halite 2.Rock gypsum 3.Limestone- can be any color, fine grained, calcite (will fizz in acid) 4.Dolostone- similar to limestone, but made of dolomite (will not fizz in acid)

Rock Salt

Gypsum

Limestone

Dolostone

Organic Sedimentary Rocks 1.Bituminous coal- plant remains 2.Limestone- formed from the shells of clams, corals and some algae (calcite was taken from chemical limestone) a. chalk b. coquina- made completely of shells

Bituminous Coal

Organic Limestone

Chalk

Coquina (limestone)

Sedimentary Rock Features 1.Stratification- arrangement of layers of different sediment 2.Bedding plane-plane between layers, usually horizontal, but sometimes cross bedding occurs 3. Fossils- the remains, impression or any other evidence of a plant preserved in rock 4. Ripple marks- sand patterns due to wind, wave, stream or current action

Stratification

Ginko Fossil

Sedimentary Rock Features 5. Mud cracks- form when mud dries 6. Nodules- lumps of silica in limestones 7. Concretion- lump of calcite in shale 8. Geodes- hallow lumps of silica in limestone, often have crystals inside

Mud Cracks

Nodules

Concretion

Geode

6.4 Metamorphic Rocks Metamorphism- the process by which a rock’s structure is changed by pressure, heat and moisture Metamorphic rocks: Formed from preexisting rocks called parent rocks Often resemble their parent

Metamorphic Rocks Minerals may be enlarged, re-formed or new minerals may appear Pressure forces grains together, making rocks less porous (less space between grains)

2 Types of Metamorphism 1.Regional- occurs during mountain building events Large areas experience heat and pressure 2. Local- effects much smaller area, 2 subtypes: a.Contact- igneous rock bakes surrounding rock b.Deformation- stress& friction, at faults

Rock Descriptions Identification is often based on parent rock, mineral content and texture Foliation- the tendency of metamorphic rocks to form bands of minerals or split along parallel layers

Metamorphic Rock Types 1. Quartzite- parent rock is sandstone (a sedimentary rock made of sand sized quartz sediment), much more dense than sandstone 2. Marble- parent- limestone (a sedimentary rock made of calcite- fizzes in acid), impurities show as wavy lines, usually fine grained with a sugary texture

Metamorphic Rock Types 2 3. Shale series- shale is a sedimentary rock made of clay sized sediment (very small)- all foliated Shale  Slate  Phyllite  Schist  Gneiss

Shale Series A. Slate- lowest metamorphism- foliated layers, mineral grains usually cannot be identified B. Phyllite- similar to slate, but is usually shiny due to mica grains becoming larger C. Schist- can also be parented by basalt, mineral grains are usually much larger D. Gneiss- parents can include shale, granite and conglomerate- high grade metamorphism, has a banded appearance