Earth and Life Science - Lesson

Types of Rocks

Igneous Rocks

-Ignis – “fire”

-Formed by volcanic activity

Types of Igneous Rocks

Extrusive Igneous Rocks or Volcanic -Solidifies at the surface

Intrusive Igneous Rocks or plutonic -Formed at depth

Characterized by:

Texture -size, shape and arrangement of interlocking crystals

Rate of cooling strongly influences crystal size. Slow cooling leads to formation of large crystals while rapid cooling results in smaller crystals:

Coarse-grained       Can be seen w/ bare eyes

Medium-grained    Can only be seen with hand lens

Fine-grained           Can only be seen through the microscope

Mineral composition -based of the chemical makeup of the parent magma

Sedimentary Rocks

Sediments result from uplifting and weathering, which are then transported and deposited into different areas.

Lithification -the process which the sediments are trans-formed into solid sedimentary rock

Compaction- as piles of sediments accumulate, the materials below are compacted by the weight of the overlying layers, as grains are pressed, pore space is greatly minimized, reducing the volume

Cementation-cement particles settle into sediment grains, fills the open spaces and then binds the particles together

As layer upon layer of sediments are accumulated, they carry with them the records of the nature of the environment as the time the sediments are deposited. These layers are called Strata. Fossils are only found in sedimentary rocks

Types of Sedimentary Rocks

Detrimental Sedimentary Rocks -these rocks came from weathered rocks such as igneous rocks

Chemical Sedimentary Rocks -these rocks came from soluble materials produced largely by chemical weathering

Metamorphic Rocks

-came from preexisting rocks called parent rocks

The preexisting rocks may undergo changes in the mineralogy, texture (grain size) & chemical composition.

Metamorphism -process of the transformation of the parent rocks

Agents of Metamorphism

Heat -heat causes chemical reactions that result in recrystallization of existing minerals &/or formation of new mineral

Pressure or stress-pressure causes space between mineral grains in the buried rocks to close, producing a more compact rock w/ higher density

Chemical agents -they act as catalyst to promote crystallization by enhancing ion migrations that may change the composition of the rock