What is a Rock? A rock is composed of many minerals. It is formed by magma and lava.

What are the three different types of rocks?
the three types of rocks are igneous sedimentary and metamorphic.

How does each type form?
  • Igneous form by magma cooling or becoming a solid.
  • Sedimentary rocks form from compaction and cementation of fragments of pre-existing rocks or plant and animals remains.
  • Metamorphic rocks form by heat, pressure, and stress.

What properties are used to identify each type of rock?

Examples of each type of rock.
igneous rock - obsidian
sedimentary rock -
metamorphic rock -

Explanation of the rock cycle.

what is a metamorphic rock?

  • Metamorphic rocks have been modified by heat, pressure and chemical process usually while buried deep below Earth's surface. Exposure to these extreme conditions has altered the mineralogy, texture and chemical composition of the rocks. There are two basic types of metamorphic rocks: 1) foliated metamorphic rocks such as gneiss, phyllite, schist and slate which have a layered or banded appearance that is produced by exposure to heat and directed pressure; and, 2) non-foliated metamorphic rocks such as marble and quartzite which do not have a layered or banded appearance. Metamorphic rocks are rocks that have changed from one form to another.
  • These rocks form deep in the earth where it is very hot and there is a lot of pressure.
  • If a rock is heated and squeezed for millions of years, it can turn into a new kind of rock.

The term metamorphism means to change

- metamorphic rocks are classified in 2 textual groups(foliated and nonfoliated)

Types of metamorphism

Thermal metamorphic involves the heating and structural and chemical alteration of rocks through processes associated with plate tectonics. This type of metamorphism has two sub-categories:
regional metamorphism is the large scale heating and modification of existing rock through the creation of plutons at tectonic zones of subduction. It involves large areas and large volumes of rock.
Contact metamorphism the small scale heating and alteration of rock by way of a localized igneous intrusion (for example, volcanic dykes or sills).

Dynamic metamorphism causes only the structural alteration of rock through pressure. The minerals in the altered rocks do not change chemically. The extreme pressures associated with mountain building can cause this type of metamorphism.

Metasomatic metamorphism involves the chemical replacement of elements in rock minerals when gases and liquids permeate into bedrock.


Some examples of metamorphic rocks are
- limestone changed into marble
  • Marble is formed when heat and pressure are applied to limestone for many thousands of years.
  • How does limestone change into marble?

    • High heat and pressure cause the calcite in the limestone to recrystallize into larger crystal structures.
- Shale turning into slate
  • Can shale change into slate?
    • Yes. Slate is metamorphosed shale or mudstone. The metamorphoses is caused by heat and pressure from depth of burial or plate collisions.
    - Granite being changed into gneiss
  • Extreme heat and pressure causes the metamorphism into gneissfrom granite, the constituent minerals recrystallize into bands, usually alternating from light colored to dark, perpendicular to the direction of the pressure which is being applied.
- sandstone turning into quartzite.
  • What is quartzite in relation to sandstone?
  • Quartzite is metamorphosed sandstone.

Metamorphic Textures
    • Foliation is a broad term referring to the alignment of sheet-like minerals. Types of foliation:
      • Schistosity - alignment of large mica flakes, as in a mica schist derived from the metamorphism of shale.
      • Slaty cleavage - alignment of very fine-grained micas, as in a slate derived from the metamorphism of shale.
      • Phyllitic structure - alignment of fine-grained micas, as in a phyllite.
  • Gneissic banding - segregation of light and dark minerals into distinct layers in the rock, as in a gneiss.
These are some metamorphic rocks and their names

Some types of Metamorphic rocks.

the picture above shows how Igneous rocks are formed.

Igneous rocks are formed by the cooling and hardening of molten rocks. Intrusive (plutonic)- form below the earth` s surface. Extrusive(volcanic)- form below the earth` s surface. Texture refers to the size of crystals in igneous rocks. Intrusive(plutonic) Igneous rocks Magma is molten rock underneath the Earth` s surface. Intrusive Igneous rocks cool slowly deep within the earth and produces large crystals. Intrusive Igneous rocks will result in a very coarse (pegmatite) or coarse(phaneritic) texture (ex. granite). Extrusive (volcanic) Igneous rocks Lava is molten rock underneath the earth` s surface. Volcanic rocks lack distinct mineral grains due to rapid cooling of lava at the earth` s surface. Extrusive Igneous rocks will result in fine ( aphanitic ) texture (ex. basalt) if the cooling is instantaneous a glassy texture may form (ex. obsidian) If gas bubbles are trapped as the lava rapidly cools a vesicular texture may occur(pumice). Porphyritic Rocks contains two stages of cooling. cools first at the remaining liquid around it cools still surrounded by magma. It is then rushed. amphibolite-2.jpg Amphibolite (above) is another example of a metamorphic rock.