23 types of rocks There are 3 types of rocks found on Earth: IgneousSedimentaryMetamorphicKnowing the differences between these 3 types of rocks allows us to learn about Earth’s past.
3Igneous Rocks - Formation Igneous Rocks are formed by melting, cooling, and crystallization of other rocks.Igneous rocks form as a result of volcanic activity, hot spots, and melting that occurs in the mantle.
4Igneous rocksIgneous rocks are common along plate boundaries or mantle hot spots
5Igneous Rocks - Classification Igneous rocks are classified using their texture in the following ways:GlassyAphanitic (no visible crystals)Phaneritic (visible crystals)Porphyritic (Some visible and some not visible crystals)
6Igneous Rocks - Texture Crystal size is used to classify igneous rocks.Crystals form as the rock cools, and the crystal size can tell us a lot about its cooling history:The larger the crystals, the slower it cooled.
7Igneous Rocks - Texture Glassy igneous rocks have no crystal structure, and probably formed by very rapid cooling (such as on the surface of a lava, or when a lava enters the water.)
8Igneous Rocks - Texture Aphanitic rocks have no visible crystals, and probably formed by fast cooling above ground.
9Igneous Rocks - Texture Phaneritic rocks have visible crystals, and probably formed by slow cooling below ground.
10Igneous Rocks - Texture Porphyritic rocks have both visible and nonvisible crystals, and probably formed by two different cooling events.
11Igneous Rocks - Classification Dark igneous rocks are formed from basaltic or mafic magma. (Mafic because it contains a lot of magnesium and iron).The magma that forms these rocks is usually very hot (around 1000°C) and viscous (about the same viscosity as ketchup.)
12Igneous Rocks - Classification Light colored igneous rocks are formed from silicic (high silica content) or felsic magmas.The magmas that form these rocks is usually more cool, (lower than 850°C), and more viscous (about the viscosity of peanut butter.)
13Igneous rocks - Formations Structures and formations seen in igneous rocks include:Hexagonal columnar jointsPahoehoe lava flowsDikes, sills, and batholiths (plutons)Pillow basaltsVolcanoes
14Igneous Rocks - Examples The most common types of igneous rocks include:RhyoliteAndesiteBasaltGraniteDioriteGabbro
16Igneous rocks - StoryWhat do you know about the history of the Earth in the place where this rock was found?
17Sedimentary Rocks - Formation Sedimentary rocks are formed by weathering, erosion, deposition, compaction, and cementation of other rocks.Sedimentary rocks form in areas where water, wind, or gravity deposit sediments.
18Sedimentary rocks - formation Sedimentary rocks are likely to form in areas such as:DeltasBeachesRiversGlaciersSand dunesShallow seasDeep oceans
19Sedimentary rocks - Classification Sedimentary rocks are classified into two groups:Clastic rocksChemically formed rocks
20Sedimentary rocks – Classification Sedimentary rocks are Clastic if they are made of pieces of other rocks that have been weathered and eroded.Clastic rocks are grouped based on the size of grain that they are made from.
21Sedimentary rocks - Classification Very small particles make up mudrock.Medium sized particles make up sandstone.Large particles make up conglomerates.
22Sedimentary rocks - Classification Sedimentary rocks that form from chemical processes are called biochemical rocks (formed from living things) or Chemical precipitates (formed from lakes or shallow seas.)
23Sedimentary rocks - formations Structures and formations seen in sedimentary rocks include:StratificationCross beddingGraded beddingRipple marksMud cracksFossils
24Sedimentary rocks - Examples Some of the most common types of sedimentary rocks include:ConglomerateSandstoneShaleLimestoneGypsumOolitesChert (including black flint and red jasper)
25Sedimentary rocks - Story What do you know about the history of the Earth in the place where this rock was found?
26Metamorphic rocks - Formation Metamorphic rocks are formed by heat and pressure changing one type of rock into another type of rock.Metamorphic rocks form near lava intrusions, at plate subduction zones, and in deep mountain roots.
27Metamorphic rocks - Formation Lava intrusions can provide heat that causes metamorphic rocks to form. These small areas of metamorphic rock form from contact metamorphosis.
28Metamorphic rocks - Formation Rocks that metamorphose because of increasing heat and pressure found at plate subduction zones and in deep mountain roots form large areas of metamorphic rock through regional metamorphosis.
29Metamorphic rocks - Classification Metamorphic rocks are classified into 2 major groups:FoliatedNonfoliated
30Metamorphic rocks - Classification Foliated rocks form when differential pressure causes minerals to form in layers.These rocks will have stripes or planes that they will break easily along.These “stripes” don’t usually line up with the original bedding planes in sedimentary rocks.
31Metamorphic rocksNonfoliated metamorphic rocks formed in areas where the pressure from all sides was equal, so there is no “linear” quality to the rocks.
32Metamorphic rocks - Formations Structures and formations seen in metamorphic rocks include:FoldingPlastic deformationStretchingAlternating dark and light layers (gneissic foliation)
33Metamorphic rocks - Examples Some common types of metamorphic rock include:SlateSchistGneissAmphiboliteMarbleQuartziteMetaconglomerate