There are 3 large classifications of rocks - igneous, metamorphic, and sedimentary. Each type of rock is formed differently and can change from one type to another over time. The way rocks are formed determines how we classify them.
- Forms when molten rock (magma or lava) cools and hardens.
- If cooling takes place slowly beneath Earth's surface, the igneous rock is called intrusive.
- If the cooling takes place rapidly on Earth's surface, the igneous rock is called extrusive.
- Forms when rocks are changed into different kinds of rocks by great heat and/or pressure - they are heated, squeezed, folded, or chemically changed by contact with hot fluids and/or tectonic forces.
- When heat and pressure reach the rock's melting point, it melts into magma.
- Forms from the compaction and/or cementation of rock pieces, mineral grains, or shell fragments called sediments.
- Sediments are formed through the processes of weathering and erosion of rocks exposed at Earth's surface.
- Sedimentary rocks can also form from the chemical depositing of materials that were once dissolved in water.
The rock cycle is an ongoing process. The sample diagram illustrates the series of natural processes that can change rocks from one kind to another.
- Rocks are used form building and construction based on their properties. What are some common building materials and what are their specific properties that make them useful for construction?
- When slow cooling magma is ejected before it has completely cools, the resulting igneous rock will have a mixture of macroscopic and microscopic mineral crystals (porphyritic texture: both intrusive and extrusive features). What are some real-world examples of these igneous rocks and what do they look like?