There are three main types of rock.

The first is igneous. Igneous means fire. There are two categories of igneous rocks: intrusive and extrusive.

Intrusive Rock Intrusions are liquid rock that forms under Earth's surface. Magma from under the surface is slowly pushed up from deep within the earth into any cracks or spaces it can find, sometimes pushing existing rock out of the way, a process that can take millions of years.

Devil’s Tower is a National Monument in the States. Scientists agree that it is an intrusion that happened in the sedimentary rocks under an enormous inland sea hundreds of millions of years ago. The sea and all the sedimentary rocks around this intrusion were washed away millions of years ago.

Extrusive Rocks Intrusions are just one of two ways igneous rock is formed. The other is extrusive. This is where the rock is formed above the surface of the ground during explosions such as volcanoes.

There are many different types of igneous rocks.

Granite This rock is made of feldspar, quartz, mica and muscovite.

Granite can come in many colours: Red, pink, yellow, brown, grey or white.

Obsidian is another igneous rock made by volcanoes. American Indians used it to make arrowheads for their spears and arrows.

Basalt is an igneous rock that has a very dark colour.

Giant’s Causeway is made of basalt.

Metamorphic Rocks Morph means to change in form. They are rocks that have changed under pressure or heat. Metamorphic rocks make up most of the Earth’s crust.

There are many different types of metamorphic rocks.

There are many metamorphic rocks in the Highlands. Gneiss Slate

Marble and Quartzite

Metamorphic rock is identified by its texture: It is either foliated or non-foliated. Foliated Non-Foliated

An abandoned slate quarry in Wales In foliated rocks, you see bands or layers. Sometimes the rocks can be flaked when they are struck. For example slate, which is used to tile roofs in the Highlands is foliated in layers which can be flaked into tiles.

The third type of rock is sedimentary rock. Sedimentary rocks are all the rocks formed by the deposition of materials on the Earth’s surface—under water or on land.

Sedimentary rocks are made up of other rocks, clay particles, sand grains, dissolved chemicals and sometimes even boulder-sized fragments. They sometimes have many layers.. They’re also sometimes mixed with remains of living organisms. Fossils are found in sedimentary rocks.

There are many types of sedimentary rock. A conglomerate is made up of rounded pebbles cemented together. Breccia is made up of angular pebbles cemented together.

Sandstones are most commonly made of feldspar and quartz. Sandstone is the most common type of sedimentary rock. In the Highlands, oil is found in shale beds under the North Sea. Sandstone is made of particles of sand cemented together. Siltstone and shale have even tiny particles of sand cemented together.

Use this link to find a rock key which will help you identify rocks. op/rockkey/index.html#rocks

All rocks are made of 2 or more minerals, but minerals are not made of rocks. A mineral is the same all the way through. There are 3000 minerals on Earth.

Feldspars Feldspars makes up about 60% of the crust. They are the most common group of minerals and are often found in metamorphic rock. It can also crystallise in veins of igneous rock.

The speed that feldspar cools, decides the size of the crystals in the rock. When it cools quickly, the feldspar is smooth. When it cools slowly, the felspar has larger cyrstals.

Other common minerals are coal, copper, diamonds, cement, garnets, gold, iodine, limestone, mercury, mica, salt, peat, quartz, silver, nickel, talc and tin. Man has been mining minerals fro thousands of years to use them for many purposes.

Use this link to discover how to identify minerals. entification.html#Properties