3 types of rocks

3 types of rocks

• There are 3 types of rocks found on Earth:– Igneous– Sedimentary– Metamorphic

• Knowing the differences between these 3 types of rocks allows us to learn about Earth’s past.

Igneous 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.

Igneous rocks

• Igneous rocks are common along plate boundaries or mantle hot spots

Igneous Rocks - Classification

• Igneous rocks are classified using their texture in the following ways:– Glassy– Aphanitic (no visible crystals)– Phaneritic (visible crystals)– Porphyritic (Some visible and

some not visible crystals)

Igneous 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.

Igneous 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.)

Igneous Rocks - Texture

• Aphanitic rocks have no visible crystals, and probably formed by fast cooling above ground.

Igneous Rocks - Texture

• Phaneritic rocks have visible crystals, and probably formed by slow cooling below ground.

Igneous Rocks - Texture

• Porphyritic rocks have both visible and nonvisible crystals, and probably formed by two different cooling events.

Igneous 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.)

Igneous 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.)

Igneous rocks - Formations• Structures and

formations seen in igneous rocks include: – Hexagonal columnar

joints– Pahoehoe lava flows– Dikes, sills, and

batholiths (plutons)– Pillow basalts– Volcanoes

Igneous Rocks - Examples

• The most common types of igneous rocks include:– Rhyolite– Andesite– Basalt– Granite– Diorite– Gabbro

Igneous rocks charted

Igneous rocks - Story

• What do you know about the history of the Earth in the place where this rock was found?

Sedimentary 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.

Sedimentary rocks - formation

• Sedimentary rocks are likely to form in areas such as:– Deltas– Beaches– Rivers– Glaciers– Sand dunes– Shallow seas– Deep oceans

Sedimentary rocks - Classification• Sedimentary rocks are

classified into two groups:– Clastic rocks– Chemically formed rocks

Sedimentary 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.

Sedimentary rocks - Classification

• Very small particles make up mudrock.

• Medium sized particles make up sandstone.

• Large particles make up conglomerates.

Sedimentary 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.)

Sedimentary rocks - formations

• Structures and formations seen in sedimentary rocks include:– Stratification– Cross bedding– Graded bedding– Ripple marks– Mud cracks– Fossils

Sedimentary rocks - Examples• Some of the most

common types of sedimentary rocks include:– Conglomerate– Sandstone– Shale– Limestone– Gypsum– Oolites– Chert (including black

flint and red jasper)

Sedimentary rocks - Story

• What do you know about the history of the Earth in the place where this rock was found?

Metamorphic 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.

Metamorphic rocks - Formation

• Lava intrusions can provide heat that causes metamorphic rocks to form. These small areas of metamorphic rock form from contact metamorphosis.

Metamorphic 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.

Metamorphic rocks - Classification

• Metamorphic rocks are classified into 2 major groups:– Foliated– Nonfoliated

Metamorphic 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.

Metamorphic rocks

• Nonfoliated metamorphic rocks formed in areas where the pressure from all sides was equal, so there is no “linear” quality to the rocks.

Metamorphic rocks - Formations

• Structures and formations seen in metamorphic rocks include:– Folding– Plastic deformation– Stretching– Alternating dark and

light layers (gneissic foliation)

Metamorphic rocks - Examples

• Some common types of metamorphic rock include:– Slate– Schist– Gneiss– Amphibolite– Marble– Quartzite– Metaconglomerate

Metamorphic rocks - Charted

Metamorphic rocks - story

• What do you know about the history of the Earth in the place where this rock was found?