Kinds of Rocks

Igneous RocksSedimentary RocksMetamorphic Rocks

Igneous Rocks

1. Igneous rocks are formed from liquid molten rock that cool slowly and harden.Igneous means made from fire and heat.

- Extrusive igneous rocks are formed from lava expelled during volcanic eruption. They cool and harden on the earth’s surface.

- Intrusive igneous rocks are formed from magma which cool or harden slowly inside the earth.

Granite and basalt are used in concrete works such as roads, sidewalks and buildings.Granite is hard and it is crushed into gravel.

Basalt is a black rock and it is crushed into sand.

Sedimentary rocks

2. Sedimentary rocks are formed from sediments such as sand, pebbles, mud, shells and remains of dead plants and animals.They hardened into rock due to pressure of water and weight of more sediments.Categories of Sedimentary rocksa. Clastic rocks-

formed from broken fragments of pre- existing rocks and minerals.

b. Chemical rocks- formed when minerals precipitate or solidify from a solution like sea water or lake water.

c. Organic rocks- formed from accumulation of plant and animal remains.

- Limestone is made from shells of sea animals and plants. It forms only under water.

- Conglomerate is made of a mixture of smooth round stones and pebbles.

- Sandstone is made up of tiny bits of sand. It is cut into blocks and used in walls and buildings because it is strong and easy to quarry.

- Shale is made from mud and fine silt or clay. It is commonly called mudstone.

Metamorphic Rocks

Metamorphic rocks are igneous or sedimentary rocks changed by extreme heat and pressure.

Metamorphic means “to have been changed”As a volcano pushes its way up through the earth, great heat changes a sedimentary rock into metamorphic rock.

Metamorphic rocks are igneous or sedimentary rocks changed by extreme heat and pressure.

Metamorphic means “to have been changed”As a volcano pushes its way up through the earth, great heat changes a sedimentary rock into metamorphic rock.

- Marble is a metamorphic rock which comes from limestone. Minerals or impurities in the marble changes its color.

- Slate is made from shale. Slate and shale have the same colors, but they do not look alike because of how they break. Slate breaks into smooth flat sheets of rocks while shale breaks only into odd shapes.

- Quartzite comes from hard sandstone.

- Schist is made from mudstone or shale. As schist is made, some of the minerals change to become mica which make the schist shine and sparkle.