Rocks

Rocks and their uses

  • Geologists study rock formations to predict and prevent natural disasters by identifying high-risk areas and evacuating people in advance.

  • Rocks are made of different grains that fit together. Grains are made from one or more chemical compounds. These compounds are called minerals. Rocks are mixtures of different minerals.

Texture:

  • The grains in rocks can be different sizes and shapes.

  • The combination of sizes and shapes of grains is called the texture of the rock.

  • Geologists classify rocks by the minerals they contain and by looking at the texture.

Interlocking grains:

  • Rocks sometimes have grains that fit together without any gaps. these grains are called interlocking grains.

  • Interlocking grains are sometimes referred to as crystals.

  • Rocks made of interlocking grains are usually hard and do not wear away easily.

  • Other rocks contain grains which r more rounded and have gaps between them. These rocks are usually not as strong as rocks made from interlocking crystals and wear away more easily cuzskill issue.

  • These rocks are also permeable and porous bc they have gaps in between them.

Keywords:

  • Porous: Having tiny holes

  • Permeable: can let water soak thru them.

  • Mixture: Two or more substances jumbled together but not joined to each other. The substances in mixtures can often be separated from each other.

  • Compound: A substance that can be split into simpler substances bc it contains the atoms of two or more elements joined together

  • Mineral: A naturally occurring element or compound that can form distinct grains in rocks.

  • Grain: A distinct part of a rock, made up of one or more minerals

  • Rock: A naturally occurring substance made of up of one or more minerals.

Igenous and Metamorphic rocks

  • We live on the crust of the Earth.

  • Underneath the crust is a layer called mantle.

  • The Earth is very hot inside. Sometimes, parts of the mantle and crust become so calor they melt. The molten rock is called magma.

Igneous rocks:

  • When molten rock cools down it freezes to form igneous rocks.

  • If molten rocks cool down fast, it forms rocks containing small crystals, such as basalt. This can happen when magma flows out of the Earth’s crust in a volcano.

  • Magma that reaches the Earth’s surface is called lava.

  • Lava cools quickly in the air or under water.

  • Rocks formed from cooling lava are called extrusive igneous rocks.

  • Large volumes of magma trapped underground will cool very slowly. This forms rocks containing large crystals, such as gabbro or granite.

  • If the magma has been forced into narrow gaps in existing rocks it can cool quickly and form rocks with small crystals.

  • Igneous rocks that form underground are called intrusive igneous rocks.

    Magma or lava can contain different combinations of substances. The kind of rock that is formed depends on the substances and on how fast it cools.

Metamorphic rocks

  • Earth’s movements can bury and compress rocks.

  • Rocks moved down into the Earth or near magma can also become more calor. High temps and pressures can cause changes in the minerals in rocks, and new crystals form.

  • Rocks changed like this r called metamorphic rocks.

  • Metamorphic rocks are always made from interlocking crystals.

  • Metamorphic usually do not share the properties of the rocks from which they were made.

  • If the rock cools slowly, there is plenty of time for a large grid pattern to form, This makes large crystals.

  • If the rock cools down quickly, there is much less time for the particles to become ordered and so smaller crystals are made.

Weathering and Erosion

Weathering

  • Weathering is a natural process that slowly breaks apart or changes rock. Heat, water, wind, living things and other natural forces causes weathering. ​

Chemical Weathering

  • Chemical weathering is cause by rain water reacting with the mineral grains in rocks to form new minerals and soluble salts. The new substance formed maybe soluble hence may wash away or be crumbly. ​

    ​

    The below is the reaction when limestone is exposed to chemical weathering: ​

    ​

    acid + metal carbonate -> salt + water + carbon dioxide

Biological weathering

  • Biological Weathering is caused by the movement of plants and animals. 

Physical Weathering

  • Physical weathering occurs when physical process affects the rock., such as changes in temperature or when the rock is exposed to effects wind, rain, ice and waves. 

Freeze thaw action

Water can get into cracks in a rock and if it freezes the ice will expand and push the cracks apart. This is called Freeze-Thaw action ​

Erosion:

Erosion is wearing away of sand, soil, rocks by water or wind. Rocks fall into stream of water where they move and knock against each other and wear away, this is called abrasion. The bits of rock and sand in streams or rivers are called sediments.

Sedimentary rocks

  • When water or air slows down, it deposits sediment. Some sediments get moved again, while others form layers.

  • Over time, more layers of sediment are deposited. The newer layers on top compress the bottom layers, forcing the grains closer together.

  • This compression squeezes out the water from the gaps between the grains.

  • When water in sediment contains dissolved minerals, these minerals can act as glue to cement the grains together.

  • Compaction and cementation transform sediments into sedimentary rocks, which are composed of grains rather than interlocking crystals.

  • The properties of sedimentary rocks are determined by the types of sediment they originated from.

  • Fossils form when dead plants or animals become covered in a layer of sediment before they rot away.