LESSON 4_ TYPES OF ROCKS Flashcards
- A naturally occurring solid mixture of one or more minerals, or organic matter
- Are classified by how they are formed, their composition, and texture
- Rocks change over time through the rock cycle
Rocks
Type of rocks
Igneous
Sedimentary
Metamorphic
Type of Rock
- Fiery
- Rocks that are formed from the solidification of molten rock material (magma or lava).
- Make up about 95% of the Earth’s crust
Igneous rocks
Type of Igneous rock
- Sometimes, magma cools slowly underneath the Earth’s surface
Example: Granite
Intrusive igneous rocks
Type of Igneous rock
- Formed from solidified lava at or near the surface of the earth.
- The fast rate of cooling/crystallization due to huge variance in the temperature between Earth’s surface and underneath
- Common textures: aphanitic, porphyritic
and vesicular
Example/s: Tuff, Obsidian, Pumice
Extrusive Igneous rocks
Type of Rock
- Small particles of sand, mud and organic material that settle to the bottom of a water or land areas
- Often lakes or oceans
- Forms when sediments (Sand, mud, organic material) accumulate over time in deposits that form layers
- These layers became squeezed and compressed over time until they consolidate into a rock
- Types of rocks in which fossils may be found since the process of forming this type of rock can preserve plant or animal remains that are deposited into the sediment layers
- ____________ processes at or near the surface of the Earth include weathering of rocks, sediment transport and deposition, compaction and cementation
Example/s: Limestone, Shale, Sandstone
Sedimentary rocks
- Means to transform
- Can involve changes in the physical and chemical properties of rocks in response to heat, pressure, and chemically active fluids.
- Can be formed by being deep under the Earth where temperature and pressures are high
- or/ When rock near the surface is heated up by the movement of tectonic plates or magma
- Different types of rocks become this type of rock when exposed to heat and pressure
- Example: Shale could turn into slate under heat and pressure. Sandstone could turn into quartzite and Limestome into marble.
Metamorphic rocks
Rock cycle
- Magma: deep beneath the Earth’s surface
- Crystallizes: Becoming Igneous rocks
- Erode: Begin the break up into smaller pieces because of wind, water or other sources. The small fragments of rock are carried away as sediment when water passes over them and are deposited into layers, which become into sedimentary rocks
- Some sedimentary rocks are then pushed below the surface due to tectonic activity where they are exposed to heat and pressure, transforming them into metamorphic rocks.
- If the rocks are buried even deeper, they may melt and form magma, starting the cycle all over again
Magma->Igneous->Sedimentary->Metamorphic->repeat
Under Extrusive Igneous Rocks
- Indicates that the magma sat and cooled a bit below the Earth’s surface, thus giving time for the last crystals to grow, before erupting onto the surface and cooling very quickly.
- The lasrge crystals are called Phenocrysts
Porphyritic texture
Under Extrusive Igneous Rocks
- Mineral grains smaller than 1mm
- Consists of small crystals that cannot be seen with the naked eye
- This texture resulted from rapid cooling in volcanic or hypabyssal (shallow subsurface) environments
Aphanatic texture
Under Extrusive Igneous Rocks
- Characterized by a rock being pitted with many cavities (known as vesicles) at its surface and inside
- Common in** aphanitic or glassy igneous rocks that have come to the surface of the Earth (Extrusion**)
Vesicular texture
Igneous rocks can be categorized based on their…
Texture and Mineral composition
Category of Igneous rock’s silica content
- Also called granitic
- > 65% silica
- Generally light-colored
Felsic (Granitic)
Category of Igneous rock’s silica content
- Also called andesitic
- 55-65% silica; generally
- Medium colored (medium gray)
Intermediate (Andesetic)
Category of Igneous rock’s silica content
- Also called Basaltic
- 45-55% silica
- Generally dark colored
Mafic (Basaltic)
Category of Igneous rock’s silica content
- <45% silica
- Generally, very dark colored; composed mainly of olivine and pyroxene which are the major constituents of the upper mantle
Ultramafic
Types of Sedimentary rocks
- Formed from the accumulation and lithification of sediments derived from the breakdown of pre-existing rocks.
- They are further classified according to dominant grain size.
Ex: Shale, Sandstone, Conglomerate
Clastic
- Derived from sediments that precipitated from concentrated solutions (e.g., seawater) or from the **accumulation of biologic or organic material **(e.g., shells, plant material).
- They are further classified based on chemical composition.
Non- Clastic
Under Non- Clastic Sedimentary rocks
Minerals crystallize out of solution to become a rock
Ex: Gypsum, Halite
Chemical Sedimentary
Under Non- Clastic Sedimentary rocks
Remains of plants and animals
Ex: Anthracite coal, Chalk
Organic Sedimentary
Type of Metamorphic rock
- Heat as the main factor: occurs when a pre-existing rocks get in contact with a heat source (magma)
- Occurs on a relatively small scale: around the vicinity of intruding magma
- Creates non-foliated metamorphic rocks
Ex: Hornfels
Contact Metamorphism
- Pressure as main factor, it occurs in areas that have undergone deformation during orogenic event resulting in mountain belts
- Occurs in a regional/large scale
- Creates foliated metamorphic rocks
Ex: Schist and Gneiss
Regional Metamorphism
