Rocks and the rock cycle man!

Rocks vs. Minerals Most rocks are composed of more than one mineral Polymineralic= rocks containing more than one mineral Ex: Granite- has quartz, feldspar, mica and hornblende “Monomineralic”=a rock composed of only one Example: Halite Some rocks don’t contain ANY minerals: Ex: Coal – made from organic matter (dead plant remains)

Types of Rocks Rocks are first classified into three groups according to how they formed 1.)Igneous- solidification of molten rock 2.)Metamorphic-recrystalization with ↑ T & P 3.)Sedimentary- compaction and cementation Rocks are further classified according to : texture and mineral content

The rock cycle

Driving forces of the Rock cycle: 1.) Heat from earth’s interior For metamorphism For the motions of the plates (lithosphere) 2.) Energy from the sun 3.) Meteorite Impacts 4.)Gravity *All of these forces create: Uplift (rocks moving to surface), erosion, weathering, pressure and melting

Sedimentary Rocks

Sedimentary Rocks 3 types: Clastic, Chemical, Biologic Most formed from Burial, Compaction, & Cementation of weathered down material (gravels, sands, clay) Sed. Rocks can be made from ANY type of other rock fragments (clasts)

How It all Starts: Weathering and Erosion: Running water erodes pre-existing rock and carries these sediments into rivers, lakes, and oceans Deposition:These sediments are then dumped, and form flat “layers” as new sediment is continually deposited Compaction: As sediments compress the layers are dewatered as water in the pore space is squeezed out

What holds it all together? Cementation: dissolved minerals precipitate out in the saturated water of pore spaces in sediments This is the “Glue” of the rock! Common cements in rock: calcite, quartz, hematite (brown/red)

1.)Inorganic Clastic Rocks – contain mostly solid sediments cemented together Conglomerate- made of many different clasts Sandstone- made of sand Shale-made of tiny pieces of clay

Breccia Vs. Conglomerate ↓ ↓

2.)Chemical Rocks Evaporites When minerals precipitate (drop) out of water and form intergrown crystals Remember, Minerals Precipitate when: 1.) Evaporation occurs (halite) AND 2.)Saturation Occurs (calcite, gypsum)

Organic (living) Reactions 3.) Bioclastic or Biologic rocks: Form when living organisms take in dissolved minerals Ex: A clam makes a shell A coral makes a skeleton You make bones and teeth When these organisms die, their material is buried, compacted, and cemented the same, but it is biologic material

Bioclastic Rocks Coquina Fossil Limestone (made of shells) Coal: Made of plant matter

Sedimentary Rocks are further classified by: (1) Grain Size Coarse: pebbles, cobbles, boulders Sand (0.0060.2 (cm) Silt (0.004  0.006 (cm) Clay ( < 0.004 (cm) (2) What the mineral composition is Ex: Limestone is composed of calcite

Igneous Rocks

Igneous Rocks “from fire” These rocks form the solidification of molten rock Magma- molten rock BENEATH the surface Lava- molten rock that goes above the surface The Texture mainly depends upon how fast the molten rock cools Fast= fine grained; small crystals; smooth Ex: Rhyolite Slow=course grained; large crystals; rough Ex: Granite

Igneous Rocks and Texture Intrusive or “Plutonic” rocks- will have Coarse grains or larger crystals Extrusive or “Volcanic” rocks- will have fine grains or small crystals

Pegmatites Igneous rocks with extremely coarse texture (large crystals)

Glassy Texture/Non Crystalline When a mineral cools so fast that crystals do not have time to form Example: Obsidian

Vesicular Texture Some molten rock contains volatiles (gases) trapped inside When the gas releases, bubble like features are recorded in the rock this is called “Vesicular Texture” Ex: Scoria Ex: pumice

Igneous Rocks and Composition Mineral Composition (1) Felsic- are rocks rich in Al and Si minerals like K-feldspar and quartz and LIGHT in color Ex: Granite and Rhyolite (2) Mafic- are rocks rich in Mg and Fe minerals like pyroxene, olivine, & hornblende and are DARK in color

Can a rock be neither felsic or mafic? YES Igneous rocks like: Andesite  Diorite  Both have roughly the same amounts of mafic and felsic minerals

The heat is on! The pressure is on! Metamorphic Rocks The heat is on! The pressure is on!

Metamorphism= ↑ T & P Any existing rock can be metamorphosed with ↑ T & P ex: LimestoneMarble The “parent rock” becomes recrystallized ↑ the size of crystals/grains new minerals form

Two types of Metamorphism 1.) Contact Metamorphism: rocks come into contact with magma/lava of an instrusion/extrusion With this supplied heat, rocks metamorphose *These rocks show no foliation because not much change in P

2.) Regional Metamorphism Sections of the lithosphere (called plates) converge/collide over long periods of time and 10’s of (km) deep The rocks at these collision zones are under very high P These rocks show different texture than contact metamorphic rocks due to high P

Textures Foliated- Non-Foliated- Have layers of crystals formed by recrystallization where minerals “align” under high P (Regional M) Non-Foliated- Are NOT layered because they were not subject to high directional P

Banding=Extreme Foliation Extremely high P causes recrystallization to form thick bands of minerals Example: Gneiss

Metamorphic Identification ShaleSlate (thin foliations, no visible crystals) ↑T & P: Slate Phyllite (shiny surface: has mica )

3.)Phyllite  Schist (higher % mica) 4.)Schist  Gneiss (extreme foliation)

Non-foliated identification Conglomerate  Metaconglomerate

*composition* is the key to identification in non-foliated rocks Usually made of one mineral Marble is metamorphosed Limestone (calcite) or dolostone so it will fizz with HCL Quartzite is metamorphosed sandstone and will easily scratch glass Anthracite Coal is usually shiny and black