Edusmart Notes on Rocks and Rock Cycle:
Rocks are made of different minerals and formed/shaped differently by Earth.
3 main groups of rocks: igneous, sedimentary, and metamorphic rocks
Igneous Rocks:
 Example – granite
 Formed when molten rock cools
 Under Earths crust some places can melt rock
 Intrusive Igneous Rock
o Formed when molten rock /magma hardens below the Earth’s surface
o Can be exposed to Earth’s surface after millions of years in process such as mountain-building and
erosion
 Extrusive Igneous Rock
o Formed when magma reaches Earth’s surface as lava and cools quickly
o Fine-grained and small mineral crystals
o Example – Pumice
o Example: Obsidian – black shiny with glass texture sometimes used to make jewelry; also used for
sharp weapon blades in ancient civilization
Sedimentary Rocks:
 Rocks are broken down into tiny pieces through weathering
 These tiny particles (pebbles, sand, clay) are eroded away by wind, moving water, and ice
o Deposition – settling down of sediments as speed of flowing water decreases
 Deposited layer by layer over thousands of years
o Compaction – sediments squeezed particles together from combined weight of many built up layers
o Cementation – dissolved minerals get deposited in space between sediment layers binding them
securely together
 Clastic sedimentary rocks (ex. Limestone and shale)
 Nonclastic sedimentary rocks (ex. Coal and limestone)
 Chemical sedimentary rocks
o Formed in shallow parts of sea and ocean where rate of evaporation is high
o Examples – limestone walls
Metamorphic Rocks:
 Forms when mineral crystals that make up existing rocks have been changed by heat and pressure
o Can be formed at boundaries of tectonic plates
o Regional metamorphosis – large plate tectonic area is transformed into metamorphic rock
 Example – limestone to marble
o Contact metamorphism heat coming from region of magma under Earth’s crust transform surrounding
rock to metamorphic rock
Rock cycle – continuous transformation of recycling of rock types