Rocks
By Gabriella Arendes
Types of Rocks
All rocks are composed of minerals, rocks are classified by the way that they are formed and where they are formed. There are three types of rocks, Igneous, Sedimentary and metamorphic rocks.
Igneous Rocks
Igneous rocks are formed by the cooling and solidification of magma. The crystal size of the rock depends on how fast the rock cools. The faster a rock cools the smaller the crystals will be and the slower the rocks cool the larger the crystals will be. Igneous rocks can be found inside the earths crust or at the Earths surface. A very popular igneous rock is granite.
Sedimentary Rock
Sedimentary rocks are formed from compaction and cementing of sediments. Most sedimentary rocks are formed from weathered or broken remains of other rocks. These types of rocks are found at or near the Earths surface, they are the only kind of rock to contain fossils. Types of sedimentary rocks are limestone, shale, and sandstone.
Metamorphic rock
Metamorphic rocks are formed when rocks are exposed to heat and/or pressure without melting. Most metamorphic rocks are formed deep within the earths surface. Foliation is caused in many metamorphic rocks which cases the layers to be wavy. Foliation is the alignment of the minerals in the rock and banding is a type of foliation that is wavy colored stripes. Types of metamorphic rocks are slate, shist, and marble.
Example of rocks
Granite
- Intrusive; forms in side the Earths, cools slowly
- Coarse, 1mm to 10mm
- Non- Vesicular
- Felsic, light, lower
- 10% Amphibole
- 20% Biotite
- 40% Quartz
- 20% Potassium Feldspar
Breccia
- Inorganic
- Pebbles, cobbles, and/or boulders embedded in sand, clay, silt
- Mostly quartz, feldspar, and clay minerals; may contain fragments of other rocks and minerals
- Angular fragments
Phyllite
- Foliated
- Fine to medium
- Contains mica, quartz, fledspar, amphibole, pyroxene
- Regional ( heat and pressure increases)
- Foliation surfaces shiny from microscopic mica crystals
The Rock cycle
The rock cycle is a model showing how rocks are formed. There are internal processes that occur in Earth and external processes that occur on Earth.