L3.1: Types of Rocks

• TYPES OF ROCKS

  - Rocks are a naturally formed, non-living earth material. Rocks are made of collections of mineral grains that are held together in a firm, solid mass.

  - Simplified: Solid, naturally occurring, inorganic/organic, and made of minerals.
• Igneous

  ● Origin

  ○ Intrusive (Plutonic): Formed from magma inside the Earth and takes a long time to solidify into rock.

  ■ Magma is molten material below the surface of the earth.

  ■ Larger crystals because there’s more time for them to grow.

  ○ Extrusive (Volcanic): Formed from lava that is on the Earth’s surface and solidifies quickly because of exposure to cooling factors.

  ■ Lava is magma that reaches the surface during an eruption; the molten material flows on the surface of the earth as lava.

  ■ Microscopic crystals because of fast solidification.
• Igneous

  ● Size vs. Cooling time

  ○ Directly proportional: higher cooling time means larger crystals.
• Igneous

  ● Texture

  ○ Phaneritic: Large interlocking crystals.

  ○ Porphyritic: Initially solidifies inside the Earth’s surface but is interrupted due to eruption, thus the solidification finalizes outside the surface. One mineral (called the phenocryst) exhibits a grain size larger than the remainder of the minerals (called the groundmass).

  ○ Aphanitic: Fine-grained wherein minerals aren’t visible due to the fast cooling rate.
• Igneous

  • Texture

  ○ Glassy: Natural glass with few crystals and cools very rapidly, like when it’s exposed to water and not just air. ○ Vesicular: Perforated due to trapped air bubbles. ○ Pyroclastic: Materials excreted by the eruption; ash and molten blobs.
• Igneous

  ● Composition (Silica Content SiO2 )

  ○ Felsic: granitic; >65%, and generally light-colored.

  ○ Intermediate: andesitic; 55-65%, and medium (gray) colored

  ○ Mafic: basaltic; 45-55%, and is usually dark colored

  ○ Ultramafic: <45%, and is very dark colored.

  ○ Pro tip: Higher silica content means it’s lighter in color. FIMU
• Sedimentary

  ● Sediments: fragments of rocks that may have resulted from weathering and aren’t necessarily small.

  ● Formed near or above the surface of the Earth. It forms when mineral crystals and clasts of plants, animals, or rocks are compressed or naturally cemented together. Also forms when mineral crystals precipitate from water to form a rocky mass such as rock salt or cave stalactites.
• Sedimentary

  ● Formation

  ○ Weathering: the breaking down of rocks into smaller pieces either physically or chemically.

  ○ Erosion: the process of transporting sediments from one place to another.

  ○ Deposition: accumulation of rocks or laying down of the sediments.

  ○ Compaction: due to gravity, the upper layer of the layered sediments is pulled down making the lower portion more compacted.

  ○ Cementation: adhesives such as clay and silt act as a glue that combines the sediments together to form a unified rock.
• Sedimentary

  ● Classification

  ○ Clastic: formed from the eroded parts of other rocks. A mixture of different rocks due to erosion that is compacted together. Pure Rock.

  ○ Non-Clastic: sediments from preexisting rocks plus minerals, crystals, or organic matter.
• Sedimentary ● Non-clastic

  ■ Evaporites: formed from the evaporation of water leaving the dissolved minerals to further crystallize. Simplified: Like when u boil water for too long then may white things on the side of the kaserola.

  ■ Precipitates: mineral supersaturated waters start to crystallize at the bottom of the solution. High mineral concentration causes crystal formation.

  ■ Bioclastic: formed with compacted organic matter. Coal is an example because it has plants.
• Metamorphic

  ● Formed only below the surface of the Earth through the process of metamorphism with the recrystallization of minerals in rocks due to changes in pressure and temperature conditions.
• Metamorphic

  ● Contact Metamorphism

  ○ Heat and reactive fluids as the main factors

  ○ Physical contact of the source of heat with the rocks

  ○ Small scale because it needs direct contact

  ○ When in contact with the magma, they will not melt but rather they will burn.
• Metamorphic

  ● Regional Metamorphism

  ○ Pressure as the main factor.

  ○ In areas that have undergone a considerable amount of mechanical deformation and chemical recrystallization which are commonly associated with mountain belts.

  ○ Occurs in a large scale because all the rocks under the mountain range are affected by the pressure.

  ○ When two plates are moving towards each other, pressure is exerted so the rocks in between them undergo regional metamorphism.
• Metamorphic

  ● Texture

  ○ Foliation: layering or parallel arrangement of certain mineral grains that gives the rock a striped appearance. Forms when pressure squeezes the flat or elongates the minerals within a rock so they become aligned.