Rock Classification by Valerie Boland

Sedimentary Rocks

Sedimentary rocks are rocks made from fragments, or tiny pieces of rocks such as pebbles, tiny boulders, and cobbles. Sedimentary rocks are formed in the ground from deposition and the fragments are carried by bodies of water on the Earth's surface. They are compacted or "glued" together with sand, mud, and clay from the processes called compaction and cementation.

Fragmental sedimentary rocks= also known as clastic, are formed from weathering fragments that are caused by hurricanes and other natural causes. Types of fragmental sedimentary rocks are conglomerate, breccia, sandstone, siltstone and shale.

This is conglomerate, which is an example of a fragmental sedimentary rock. It has a coarse-grained texture that is made up of rounded fragments, or tiny rocks.

Chemical sedimentary rocks= also known as crystalline, are formed from minerals dissolving in water due to precipitation. Types of chemical sedimentary rocks are halite or rock salt, rock gypsum, chert, flint, some dolomites and some limestones.

This is rock salt, which is an example of a chemical sedimentary rock. It is a type of salt known as halite that is made up of mainly sodium chloride.

Organic sedimentary rocks= also known as bioclastic, are formed from the lithification and accumulation of animal and plant debris, mainly fossils. Types of organic sedimentary rocks are coal, some dolostones and some limestones.

This is organic limestone, which is an example of a bioclastic sedimentary rock. It is made up of skeletal fragments of once living organisms.
Sedimentary rocks on the rock cycle.
This is a map of all the rock locations in the United States.

Metamorphic Rocks

Metamorphic rocks are rocks made from already existing rocks from all types. They are created by heat and/or pressure underground.

This is marble, which is an example of a metamorphic rock. It comes from the sedimentary rock limestone.

Regional Metamorphism= occurs over a large area deep inside the earth's surface. It may cause the rock layers to become distorted, meaning they become wavy. The minerals inside the rocks align in bands. Metamorphic rocks that are distorted or have bands are foliated and they are recrystallized. Types of foliated metamorphic rocks are schist, slate, phyllite and gneiss.

This is schist, which is an example of a foliated metamorphic rock. It is coarse-grained with many layers of minerals.

Contact Metamorphism= occurs when the rock is changed when it is coming into contact with molten rock. It is considered a nonfoliated rock and they are composed of crystals. Types of nonfoliated metamorphic rocks are quartzite, marble, hornfels and metaconglomerate.

This is quartzite, which is an example of a nonfoliated metamorphic rock. It was created from pure quartz sandstone.
Metamorphic rocks on the rock cycle.

Igneous Rocks

Igneous rocks are rocks made from molten rock that is solidified and hardened. The word "igneous" means fire-formed.

This is obsidian, which is an example of an igneous rock. It has a glassy texture that is made from felsic lava.

Intrusive igneous rock= When magma is cooled deep in the ground. The magma cools slowly, allowing time for large crystals to form and the texture to be coarse. Types of intrusive igneous rocks are granite, pegmatite, gabbro and diorite.

This is granite, which is an example of an intrusive igneous rock. It is light in color with a coarse texture.

Extrusive igneous rock= When lava is cooled at or above the earth's surface. The lava cools quickly, so there is only time for small crystals to form and the texture to be fine. The rocks would also be porous or vesicular because air pockets were trapped in the cooling process. Types of extrusive igneous rocks are rhyolite, basalt, pumice and scoria.

This is rhyolite, which is an example of an extrusive igneous rock. It has a felsic composition with a fine texture.
Igneous rocks on the rock cycle.

Rock Tools

Streak plate= used to determine the streak color of a rock. The color of the streak is one of the most efficient way to determine a rock or mineral.

The streak plates are scratched by the rocks or minerals.

Hydrochloric acid= used to determine if a sedimentary rock is bioclastic, meaning there is a fossil present(there was an organism once living in it) called the "acid test".

This shows hydrochloric acid being dropped on a rock. If the rock bubbles, the rock is bioclastic and there was an organism once living.

Magnifying glass= used to take a closer look at the rock. It allows people to see crystals, layers, and bands in rocks easier.

The magnifying glass makes small objects or patterns look bigger, so it makes it easier to classify.
Created By
Valerie Boland


Created with images by stebulus - "rocks" • James St. John - "Conglomerate" • Hans - "obsidian stone volcanic"

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