The Earth is covered in a layer of solid rock called the crust. The three main types, or classes, of rock, are sedimentary, metamorphic, and igneous, and the differences among them have to do with how they are formed. Test your knowledge of rocks from our previous classes by taking the simple test.
Igneous, sedimentary, metamorphic
Volcanic, plutonic, extrusive
Gneiss, basalt, obsidian
From earth's internal pressure
From cooled molten magma
From the deposition of sediments
Sedimentation of particles
Weathering and erosion
Heat and pressure
Magma or lava cools, forming igneous rocks.
Extreme heat and pressure produce metamorphic rocks
Sediments are created deep beneath Earth's surface.
Extrusive igneous
Intrusive igneous
Intrusive metamorphic
Compaction, cementation, deposition, weathering, erosion
Weathering, erosion, deposition, compaction, cementation
Deposition, cementation, compaction, erosion, weathering
Cloud
Frost
Rain
People carrying them
Rivers carrying them
By exploding volcanoes
Sedimentary
Metamorphic
Igneous
Presence of crystals
Physical properties
Permeability