Rocks and Their Types - Sternberg Museum of Natureal History (2023)

Rocks and Their Types

What is a Rock?

A rock is a naturally occurring mass made of minerals. Rocks are classified by the minerals found in them and how they formed. There are three main groups of rocks: igneous, metamorphic, and sedimentary.

  • Igneous Rocks
  • Metamorphic Rocks
  • Sedimentary Rocks

...

Igneous Rocks

Igneous rocks form from molten material. If the molten material is beneath the Earth’s surface, it is called magma. If the molten material is flowing on the surface, it is called lava. Igneous rocks are classified by their composition (i.e. minerals that are present) and texture (i.e. size of mineral grains). Some igneous rocks contain minerals that are rich in iron and magnesium and tend to be darker (mafic rocks). Those that have less iron and magnesium tend to be lighter (felsic rocks). Some rocks are intermediate between mafic and felsic, and these rocks are often composed of light and dark minerals. The grain size depends on how quickly the magma or lava has cooled. If the magma cooled slowly, the individual grains had time to grow and can be seen with the eye. These rocks have a coarse-grained, or phaneritic, texture. If the magma cooled quickly, the individual grains did not have time to grow and cannot be seen with the eye. These rocks have a fine-grained, or aphanitic, texture. When the lava cools very quickly, the rock has a glassy texture. Coarse-grained rocks tend to form beneath the surface of the Earth and fine-grained rocks tend to form at the surface. Rocks formed beneath the Earth’s surface are called intrusive igneous rocks (because they are intruding into space). and those formed above the surface are called extrusive igneous rocks (because they are extruded above the surface).

Iron/magnesium poor (felsic) igneous rocks

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Intermediate igneous rocks
Common intermediate minerals are amphiboles and calcium-rich plagioclase feldspar.

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Iron/magnesium-rich (mafic) igneous rocks
Common mafic minerals are pyroxene and calcium-rich plagioclase feldspar.

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Rocks and Their Types - Sternberg Museum of Natureal History (7)

Igneous Rock Textures

  • Aphanitic – Comes from a- meaning “not” and phaner meaning “visible”. Examples of rocks with aphanitic texture are obsidian or pumice.
  • Phaneritic – Comes from phaner meaning “visible”. Examples of rocks with phaneritic texture are diorite or granite.
  • Porphyritic – Named for the texture of the rock porphyry and has a few large grains in a matrix of grains too small to see.
  • Pegmatitice –Named for the texture of the rock pegmatite and has large grains interspersed with massive grains (some centimeter to meters in size)
  • Pyroclastic – Comes from pyro meaning “igneous” and clastic meaning “fragment”. There are three types of pyroclastic igneous rocks:

Volcanic bomb – a mass of molten rock, larger than 64 mm in diameter, ejected during volcanic eruptions that cool into solid fragments before they reach the ground.

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Lapilli– In Latin means “little stones”, a mass of molten rock, between 2-64 mm in diameter, ejected during volcanic eruptions that cool into solid fragments before they reach the ground.

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Volcanic ash – a mass of molten rock, less than 2 mm in diameter, ejected during volcanic eruptions that cool into solid fragments before they reach the ground.

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Examples of igneous rocks through the different stages of felsic, intermediate, and mafic and if the rock was formed intrusively (phaneritic texture) or extrusively (aphanitic texture).

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Metamorphic Rocks

Metamorphic rocks are a result of a transformation of a pre-existing rock. The original rock is subjected to intense heat and pressure, which causes physical and, sometimes, chemical changes.Chemical reactions can also lead to a change in rocks. Unlike igneous rocks, metamorphic rocks never fully melt but instead becomemalleable like toothpaste. These rocks are often found in mountainous regions. Fossils can only be found in metamorphic rocks that are formed from sedimentary rocks under special circumstances. However, these fossils are often distorted or destroyed. Metamorphic rocks can be either foliated or non-foliated. Foliated comes from the Greek word phyllon meaning “leaf”, which refers to the thin layers in the rock due to parallel arrangements of certain mineral grains that give the rock a striped appearance. Foliation forms when pressure flattens the minerals within a rock. Non-foliated rocks are those in which the minerals are randomly arranged and the grains do not align under pressure. Non-foliated rocks also occur in contact metamorphism, which is when there is extreme heat but not pressures.

Foliated Rocks (from highly to poorly metamorphosed rock)
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Non-Foliated Rocks
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Sedimentary Rocks

Most of the Earth’s land surface is covered by sedimentary rocks. Sedimentary rocks are formed from pre-existing rocks or organic material. They form from deposits that have accumulated on the Earth’s surface over long periods of time. This leads to a distinctive layered appearance. The study of these layers is called stratigraphy. Stratigraphy allows scientists to study the history of the Earth. Fossils are preserved in many types of sedimentary rocks.

There are three main types of sedimentary rocks: clastic, chemical, and biologic. Clastic sedimentary rocks are rocks made up of pre-existing rocks. Pieces of pre-existing rocks are loosened

by weathering and erosion, and then are transported, trapped, and will accumulate over time. Sedimentologists (geologists who study sedimentary rocks) classify clastic sedimentary rocks based on their maturity using grain size, sorting, and shape. Clastic sedimentary rocks have particles that range in size. Their names are based on the grain size and are categorized into three main groups: clay (less than 1/16 mm), sand (1/16 – 2 mm), and gravel (larger than 2 mm). Grain shape ranges from angular to rounded. For example, breccia has angular grains and conglomerate has rounded grains. Grains tend to become more rounded as they weather. Grain sorting refers to variability in grain size. Are all the grains the same size or are there some large and some small grains? A combination of large and small grains is called poorly sorted. Grains of all the same size are called well sorted.

To understand how sedimentologists use grain size, shape, and sorting to determine sediment maturity, let’s imagine a box of cereal. In a new box of cereal, all of the cereal pieces are relatively big and (depending on the type of cereal) angular. As the cereal is jostled during transport, the large pieces of cereal will gradually break into smaller pieces. A cereal box filled with pieces of cereal of many different sizes has probably not been transported for very long but a cereal box with all of the pieces crumbled to dust has probably traveled a long way from where it was packaged. Immature sediments are found close to their source rock (the cereal factory). They have large, angular grains and are poorly sorted, with grains of many different sizes. Mature sediments are found far from their source rock (far from the cereal factory). They have small, rounded grains and are well sorted, meaning all the grains are about the same size.

  • Clastic Sedimentary Rocks
    • Sandstone
    • Shale
    • Conglomerate
    • Breccia

Chemical sedimentary rocks form when minerals in a solution become supersaturated and inorganically precipitate. Rocks like limestone form when the accumulation of calcium carbonate through the precipitation from seawater. Evaporites such as gypsum or halite form when shallow water evaporates and leaves behind a “residue”.

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  • Chemical Sedimentary Rocks
    • Oolites
    • Limestone

Biologic sedimentary rocks form when large numbers of living things die and collect in a basin. Examples of this include chert (made from shells of diatoms or radiolarians) or fossiliferous limestone (made from parts of fossil organisms such as shells).

  • Biologic Sedimentary Rocks
    • Chert
    • Coal
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FAQs

What are the 3 rock classes? ›

There are three main types of rocks: sedimentary, igneous, and metamorphic. Each of these rocks are formed by physical changes—such as melting, cooling, eroding, compacting, or deforming—that are part of the rock cycle. Sedimentary rocks are formed from pieces of other existing rock or organic material.

What are the building rocks? ›

Minerals are the building blocks of rocks. Nature cements combinations of minerals together to form rocks. Rocks are catagorized in three general groups according to the way they were formed.

What type of rock comes from liquid rock materials? ›

Igneous rocks form when magma (molten rock) cools and crystallizes, either at volcanoes on the surface of the Earth or while the melted rock is still inside the crust.

What are primitive rocks? ›

Primary rocks. a term early used for rocks supposed to have been first formed, being crystalline and containing no organic remains, as granite, gneiss, etc.; – called also primitive rocks.

What is rock and types? ›

There are three kinds of rock: igneous, sedimentary, and metamorphic. Igneous rocks form when molten rock (magma or lava) cools and solidifies. Sedimentary rocks originate when particles settle out of water or air, or by precipitation of minerals from water. They accumulate in layers.

Which class of rock is used in building? ›

Intrusive stone are commonly used as building stone. It is quarried under the earth's surface and comes in different types like granite, basalt and obsidian. Granite is an igneous rock that is very hard and of crystalline texture formed from quartz and orthoclase or microcline.

What are rock structures called? ›

Rock cairns are human-made stacks, mounds or piles of rocks. They take different forms, and have been built by cultures around the world for many different purposes. Cairns may serve as monuments, burial sites, navigational aids (by land or sea), or ceremonial grounds, among other uses.

What are 5 characteristics of a rock? ›

Physical Characteristics of Rocks - Cleavage, Streak, Hardness, Fracture, Luster.

How many rock types are there? ›

There are 3 types of rocks: igneous, sedimentary and metamorphic and this is how they form. Igneous rock forms when hot liquid rock called magma cools.

What is liquid rock called? ›

Magma is extremely hot liquid and semi-liquid rock located under Earth's surface. When magma flows onto Earth's surface, it is called lava.

What are the 4 rock types? ›

Contents
  • 1 Igneous rocks.
  • 2 Sedimentary rocks.
  • 3 Metamorphic rocks.
  • 4 Specific varieties.
  • 7 External links.

What are the 5 steps of rock formation? ›

Sedimentary rocks are the product of 1) weathering of preexisting rocks, 2) transport of the weathering products, 3) deposition of the material, followed by 4) compaction, and 5) cementation of the sediment to form a rock.

What is called a rock? ›

What Is a Rock? To geologists, a rock is a natural substance composed of solid crystals of different minerals that have been fused together into a solid lump. The minerals may or may not have been formed at the same time. What matters is that natural processes glued them all together.

What is a rock and example? ›

A rock is a solid collection of mineral grains that grow or become cemented together. Some rocks are large while others are small. Small rocks are called pebbles. Every rock is made up of one or more minerals. Geologists (people who study rocks and minerals) classify rocks according to the way they are formed.

What are the 7 characteristics of rocks? ›

Properties that help geologists identify a mineral in a rock are: color, hardness, luster, crystal forms, density, and cleavage. Crystal form, cleavage, and hardness are determined primarily by the crystal structure at the atomic level.

What are 4 common igneous rocks? ›

Igneous rocks can be divided into four categories based on their chemical composition: felsic, intermediate, mafic, and ultramafic.

What are the 4 properties of rocks? ›

Rock physical properties include density, porosity, and permeability, etc. Rock mechanical properties mainly include elastic modulus, Poisson's ratio, and rock strength.

What are 2 types of igneous rock? ›

Igneous rocks are divided into two groups, intrusive or extrusive, depending upon where the molten rock solidifies.

What are Class 7 rocks used for? ›

Answer: Rocks are useful for various purposes: It helps in making roads. It is used in the construction of houses and buildings. Small stones are used by children in different types of games.

What are the uses of rocks? ›

They help us to develop new technologies and are used in our everyday lives. Our use of rocks and minerals includes as building material, cosmetics, cars, roads, and appliances.

What are the 3 major types of stone used in construction? ›

It's important to know the properties and distinctions of each so you can use the right materials for your project. Of course, the three main types of natural stone are common knowledge- igneous, metamorphic, and sedimentary.

How are rocks named? ›

Origin of Names for Rocks and Minerals. The Rock and Mineral names can be traced quite often to Greek and to Latin. It is common practice to add an “ite” to a mineral name. The suffix “ite” is derived from the Greek word lithos (from its adjectival form -ites), meaning rock or stone.

What is a flat rock called? ›

FLAGSTONE: Relatively flat, it comes in various sizes and can be from 3/4 inch to 3 inches thick.

What is a tall rock called? ›

A hoodoo (also called a tent rock, fairy chimney, or earth pyramid) is a tall, thin spire of rock formed by erosion.

Which are the rocks used to build monuments? ›

Granite is the most widespread rock on the earth's crust, and thus it has been used by civilisations around the world to build long-lasting monuments, structures, and buildings.

Why rocks are used as building materials? ›

Rock is an ideal building material because of its durability, making it resistant to wear and tear.

Which rock is used in floor? ›

Metamorphic rocks

It is an extremely hard and waterproof stone. Marble is formed when limestone is subjected to higher pressure and temperature conditions, and is mainly composed of calcite and/or dolomite. Marble flooring is a very elegant option.

What are 4 ways to identify a rock? ›

To identify your rock, first take note of its physical properties like color, luster, banding, layering, and grain size.

What is rock and its properties? ›

Rocks are characterized by their composition (minerals, fluids), texture, and structure. Of specific interest are sedimentary rocks with respect to their reservoir properties. Clastic (sandstone) and carbonate (limestone, dolomite) rocks are the most common reservoir rocks.

What are the 5 classification of rocks? ›

Rocks are classified into three types based on their geological formation and they are : Sedimentary rocks. Igneous rocks. Metamorphic rocks.

Is Diamond a rock? ›

By definition, a rock is a substance made up of two or more minerals. Although they are composed of unique minerals, rocks are what we often see in nature. A rock must have at least two minerals in its composition. Diamond cannot be considered as such because it solely includes carbon.

What is the most common type of rock? ›

Sedimentary rocks are the most common rocks exposed on Earth's surface but are only a minor constituent of the entire crust, which is dominated by igneous and metamorphic rocks.

What is melted rock called? ›

Scientists use the term magma for molten rock that is underground and lava for molten rock that breaks through the Earth's surface.

What is melted rock also called? ›

lava. noun. molten rock, or magma, that erupts from volcanoes or fissures in the Earth's surface.

What is molten rock? ›

Molten rock, i.e., magma, is less dense and more buoyant than the surrounding rock, as a result magma rises through Earth's crust. Most magma is trapped in the crust, but some erupts onto the Earth's surface as lava.

What are 10 different types of rocks? ›

Rocks: Igneous, Metamorphic and Sedimentary
  • Andesite.
  • Basalt.
  • Dacite.
  • Diabase.
  • Diorite.
  • Gabbro.
  • Granite.
  • Obsidian.

What is the 9 major rock forming types? ›

The rock-forming minerals are: feldspars, quartz, amphiboles, micas, olivine, garnet, calcite, pyroxenes. Minerals occurring within a rock in small quantities are referred to as “accessory minerals”.

What are the examples of secondary rocks? ›

The most common secondary minerals are Kaolinite (chemical weathering of Feldspar), Chlorite (weathering of Biotite, Pyroxene, and Amphibole), Sericite (weathering of feldspar), and Serpentine (hydrothermal modification of Olivine).

Which rock is called primary rock Why? ›

1. Igneous rocks- formed by the cooling and solidification of magma (molten rocks). It begins the rock cycle. So, it is known as primary rocks.

What is class 5 rock cycle? ›

A rock cycle is a fundamental concept that shows the transitions among the three basic rock types (metamorphic, igneous and sedimentary). In simple terms, it is a chain of processes that produce and transform the rock types in Earth's crust.

What is the best rock for building? ›

Sedimentary Rocks

Sedimentary stones are known for their many qualities, including their strength, durability, and versatility. Most sedimentary rocks have high corrosion resistance, making them the best types of stone for building wall cladding, flooring, fireplaces, and more.

What rocks are used to build walls? ›

The most typical stone for constructing walls in the United States is sandstone, limestone, granite, and fieldstone. In addition, concrete blocks designed to look like natural stone can make an effective stone wall.

Which type of rock is best for foundation? ›

Foundation is the natural material on which the building rests. Generally base rock, especially of igneous origin, is the strongest foundation material.

What are rock building minerals? ›

The rock-forming minerals are: feldspars, quartz, amphiboles, micas, olivine, garnet, calcite, pyroxenes. Minerals occurring within a rock in small quantities are referred to as “accessory minerals”.

Which type of rock is most durable? ›

Metamorphic rocks have been subjected to tremendous heat and/or pressure, causing them to change into another type of rock. They are usually resistant to weathering and erosion and are therefore very hard-wearing.

Which type of rock is most resistant? ›

Quartz is known to be the most resistant rock- forming mineral during surface weathering.

What type of rock is used for painting? ›

Avoid buying rocks that have a wax film over them to make them shiny. This makes it difficult for paint or markers to adhere to the rock. Amazon has some great rocks for painting: Capcouriers white rocks.

Which rock is used for Jewellery? ›

Granite is a light-colored igneous rock. It is composed mainly of quartz and feldspar with a little amount of mica, amphiboles and other minerals. Granite is the world's toughest substance and is used in jewelry making.

Which rock is used to make brick? ›

Clay Bricks

The main ingredient of bricks is clay, a group of surface minerals that arise from the weathering of igneous rocks. By itself, clay is not useless—making bricks of plain clay and drying them in the sun makes a sturdy building "stone." Having some sand in the mix helps keep these bricks from cracking.

What is white rock called? ›

Collectively, White Rocks is composed of intrusive igneous rock, meaning the rock crystalized from molten magma as it slowly cooled beneath the surface of the Earth.

What type of rock is concrete? ›

Limestone rocks fall under the category of sedimentary rocks that are made from mineral calcite. This rock is used to make concrete and is an excellent building stone for humid regions. Limestone, chemical formula CaCO3, is a white, chalky solid in most conditions.

What are the 7 common minerals? ›

There are many known mineral species, but the vast majority of rocks are formed by combinations of a few common minerals, called “rock-forming minerals.” The minerals that form rock are: feldspar, quartz, amphiboles, micas, olivine, grenade, calcite, pyroxenes.

What are the 4 uses of rock? ›

Our use of rocks and minerals includes as building material, cosmetics, cars, roads, and appliances. In order maintain a healthy lifestyle and strengthen the body, humans need to consume minerals daily.

What are the 5 most common minerals? ›

The most common minerals on Earth are quartz, feldspar, mica, amphibole (such as hornblende), and olivine. Minerals are usually classified as either metallic or nonmetallic.

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