Rock (geology)

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They are made of tiny bits called minerals. \n\nSome rocks form from hot liquid. This liquid cools and turns hard.

\n\nOther rocks form from bits of sand. These bits settle in layers. \n\nSome rocks change from old ones. Heat and heavy weight change them. \n\nPeople use rocks for many things. They use them to build houses.

Rocks are all around us.", "media": [ "File:Kummakivi balancing rock in Ruokolahti, Finland.jpg", "File:GabbroRockCreek1.jpg", "File:\"Liesegang banding\" in quartzose sandstone (Upper Paleozoic; quarry near Crossville, Tennessee, USA) (2.jpg)", "File:Pirunvuoren kivilinna.jpg" ] }

Rocks are solid masses that make up the Earth's crust.

They are made of minerals. Minerals are tiny, solid parts that fit together in an orderly way. Most rocks also contain silicate minerals. These are parts that include silica.

Rocks usually fall into three main groups. The first is igneous rock. These form when hot magma or lava cools down and turns hard.

The second group is sedimentary rock. These form when bits of sand or shells settle in layers. Over time, these layers press together to make stone. Some sedimentary rocks even hold fossils. The third group is metamorphic rock. These form when heat and heavy pressure change an old rock. This change happens without the rock melting.

Humans have used rocks for a very long time. Early people used them to make tools. Later, people used them to build houses.

Today, we even make our own rocks. We call this concrete. It is a man-made rock used for building.

Rocks are solid masses that make up the Earth's crust.

They are made of minerals, which are tiny crystals held together in an orderly way. Most rocks contain silicate minerals, which include silica.

These minerals decide the name and properties of a rock. Some rocks also contain mineraloids, like volcanic glass. These are rigid but do not have a crystal structure. Rocks form the outer layer of our planet. They also make up most of the interior. The only parts without rock are the liquid outer core and magma pockets.

Rocks change through a process called the rock cycle. Igneous rocks form when magma or lava cools and hardens. If it cools slowly underground, it is called an intrusive rock, like granite. If it reaches the surface, it is an extrusive rock, like basalt.

Sedimentary rocks form at the surface. Bits of older rocks, minerals, or even living things settle in layers. Over time, pressure and cementation turn these layers into stone. Metamorphic rocks form when existing rocks face high heat and pressure. This happens without the rock melting completely. This change is called metamorphism.

People have used rocks for a very long time. The Stone Age was a period when early humans made many stone tools.

Later, rocks became important for building houses and infrastructure. Mining grew so people could find metals inside rocks. This helped human society advance. Today, we even make our own rocks. Concrete is a human-made rock used for building. It has been around since Ancient Rome. Some people call these "anthropic rocks."

Scientists study rocks using different branches of geology. Petrology is the study of how rocks form and their character. Mineralogy is the study of the minerals that make them. The formal science of geology grew in the 19th century. In 1896, scientists discovered radioactive decay. This allowed them to use radiometric dating to find a rock's age. Later, in the second half of the 20th century, people learned about plate tectonics. This helped explain how the Earth's surface moves and changes.

Rocks are not just found on Earth. Many other objects in space are made of rock. Mars, Venus, and Mercury are all rocky worlds.

Asteroids and meteoroids are also made of rock. When a meteorite falls to Earth, it provides clues about space. Some rocks from space even come to Earth through missions like Hayabusa. You can see how rocks work by looking at the Grand Canyon. The layers there show how many different types of rocks have formed over time.

A rock is a naturally occurring solid mass or aggregate of minerals.

Most rocks are made of mineral grains, which are crystalline solids. These solids form from atoms bonded into an orderly structure. Some rocks also contain mineraloids. These are rigid, mineral-like substances like volcanic glass that lack a crystalline structure. Rocks form the Earth's crust and much of its interior. The only parts without rock are the liquid outer core and magma pockets in the asthenosphere.

Geologists study rocks through several specialized branches. Petrology is the study of the character and origin of rocks. Mineralogy is the study of the mineral components that create them. Most rocks contain silicate minerals, which include silica tetrahedra in their crystal lattice. These minerals make up about one-third of all known mineral species. They also account for about 95% of the Earth's crust. The amount of silica in a rock is a major factor in its properties.

Rocks are classified into three main groups based on how they form. The first group is igneous rock, which comes from the Latin word for fire. These rocks form when magma or lava cools and solidifies. Magma can come from the partial melting of existing rocks. This melting happens due to increased temperature, decreased pressure, or changes in composition. Igneous rocks are divided into intrusive and extrusive types. Intrusive, or plutonic, rocks like granite cool slowly inside the crust. Extrusive, or volcanic, rocks like basalt or pumice form on the surface.

The second group is sedimentary rock, which forms at the Earth's surface. This happens through the accumulation of fragments from older rocks, minerals, or organisms. These fragments are called sediments. Weathering and erosion break down existing rocks into these pieces. Then, agents like water, wind, or ice transport them to a new place. Once deposited, the particles undergo compaction and cementation. This process is called diagenesis or lithification. Sedimentary rocks often form in horizontal layers called strata.

The third group is metamorphic rock, which forms through a process called metamorphism. This means a "change in form." Any rock type can become metamorphic if it faces extreme heat and pressure. This process happens without the rock melting completely. The original rock is called a protolith. High temperatures and pressures cause the rock to undergo recrystallization. This changes its physical properties and chemistry. For example, contact metamorphism is caused by heat from nearby magma. Regional metamorphism occurs in large areas, often during mountain building.

Metamorphic rocks can be divided into foliated and non-foliated types. Foliated rocks, such as schist or gneiss, have a layered or banded texture. Non-foliated rocks, like marble or quartzite, do not have this texture. The history of studying these rocks grew significantly in the 19th century. During this time, the theory of plutonism was developed. In 1896, the discovery of radioactive decay changed everything. This allowed scientists to use radiometric dating to find the age of rocks. Later, in the 20th century, we developed an understanding of plate tectonics.

Humans have used rocks for at least 2.5 million years. During the Stone Age, early humans developed many stone tools. Later, mining became essential to extract metals from rocks. This helped human technology and society advance. Today, we even create "anthropic rocks," which are human-made. Concrete is a famous example of an anthropic rock. It has been used for construction since Ancient Rome. Rocks vary greatly in strength. Some, like quartzite, are very strong. Others are so soft they can be crumbled by hand.

Rocks are not limited to our planet. Many celestial bodies in the solar system are made of rock. Mars, Venus, and Mercury are all rocky worlds. Asteroids and meteoroids are also composed of rock. When meteorites fall to Earth, they provide evidence of extraterrestrial compositions. Scientists have even studied rocks from the Moon and Mars. Space missions, like Hayabusa, have even brought asteroid rocks back to Earth. Studying these rocks helps us understand the history of the entire universe.