What is a rock? (Activities)

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Scientifically it is a hard substance composed of one or more minerals. The most common minerals in rocks are the most abundant elements in the earth's crust.

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A rock can contain natural substances that do not always correspond to the definition of a mineral. The rocks can be made of volcanic glass or opal. Both substances have no crystal structure and are not minerals in the strictest sense of the word.

Types of rocks

To understand the enormous diversity of rocks in the world it is necessary to organize them in a logical way. Geologists group the rocks according to certain characteristics.

There are three large groups of rocks according to their formation: igneous, sedimentary and metamorphic.

The igneous rocks

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Igneous rocks form during solidification of magma. They were the first rocks on Earth. Magma is the molten substance of the mantle or crust, saturated with gases and water vapor.

The most common abyssal igneous rock is granite. It forms at great depths, where magma solidification takes a long time. The color of granite varies according to the color of the feldspars included in its composition.

Having spilled on the surface of the earth or the bottom of the oceans, lava freezes very quickly. From it igneous (volcanic) rocks are formed, for example, basalts. Basalts have a dark gray or black color and high density.

Igneous rocks are composed of mineral crystals. The faster the magma freezes, the smaller the crystals. With very rapid solidification of magma, no crystals form.

Most igneous deposits of various metals are associated with igneous rocks.

Depending on where the magma solidifies, igneous rocks are divided into intrusive and extrusive.

The sedimentary rocks

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They consist of mineral accumulations, but these minerals can have not only chemical, but also organic origin. The outer layer of the Earth is a "native home" only for sedimentary rocks: they are formed and exist in conditions of temperatures and pressures characteristic of the earth's surface.

But during the formation, for example, of igneous and metamorphic rocks, completely different conditions existed. The shell of this Earth, in which sedimentary rocks are formed and where they are located, is called stratisphere.

Sedimentary rocks arose as a result of the deposition of various substances in the aquatic environment, as a result of glacier activity.

The upper layer of the earth's crust is mainly composed of sedimentary rocks.

Metamorphic rocks

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Metamorphism is a change in the rocks under the influence of the increase in temperature and pressure, as well as various gaseous and liquid underground substances.

Metamorphic rocks are formed when chemical reactions, high heat or high pressures change existing rocks in other types of new rocks. These new rocks have physical and chemical properties usually different from the original rocks.

Examples:

• An igneous rock like granite, with metamorphism, becomes gneiss.
• A sedimentary rock like clay is transformed into shale as a result of metamorphism.
• Limestone becomes marble.
• Quartzite is a granular metamorphic rock that is formed during metamorphism from quartz sandstones.

Activities:

1. What are the three main groups of rocks? Give an example of each group.
2. How are igneous, sedimentary and metamorphic rocks formed?
3. Depending on where the magma solidifies, how do igneous rocks divide?
4. What kind of stone does clay become after metamorphism?
5. From which rock does marble come after metamorphosis.

Reference:

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