Lecture 5: Rock Types

Phenocrysts

• a large crystal in an igneous rock, found in porphyry rocks

• ex. olivine grains in basalt

sandstone

lithified sand

mid oceanic ridges

• produces the most voluminous type of volcanism (basaltic volcanism)

igneous

obsidian, porphyry

sedimentary

• calico (laminated sandstone)

• coquina (shell limestone)

• breccia - caused by weathering

metamorphic

• banded gneiss - gneissic banding that shows a horizontal separation of light and dark colored minerals

• talc schist - random foliation pag schist

• serpentine - metamorphism through chemically active fluids

mp process

• Gneiss forms under high pressure and temperature. 

• The minerals in gneiss have different densities and melting points. 

• As the rock is heated, the denser minerals sink to the bottom, while the less dense minerals float to the top. 

• This process of segregation leads to the formation of bands of different minerals. 

vesicular basalt

• extrusive/volcanic igneous rock

• contains olivine crystals

• finer grain crystals

diorite

• intrusive/plutonic igneous rock

• larger crystals

pumice

• pyroclastic igneous rock - from other volcanic materials ex. ash, lapili (volcanic fragments from the sky)

granite

contains quartz, hornblende, kfelds