Rock of the Month

Rock name: Obsidian

Rock type: Igneous

Description: Very shiny, with the appearance of natural glass.

Formation: Formed by the very fast cooling of lava.

Uses: Used for a variety of tools during the Stone Age and even now for scalpels in surgery!

Where can I see it?: Whilst obsidian does not occur in the British Isles, pitchstone, a similar rock, occurs on the Isle of Arran and the Sgùrr of Eigg.

Fun Fact: You might have come across the rock name obsidian whilst playing Minecraft!

Rock name: Conglomerate

Rock type: Sedimentary

Description: Immature clastic rock with a variety of clasts in a range of sizes.

Formation: Formed when large clasts, pebbles or cobbles are transported & deposited in a river system, with finer grained material filling the spaces in between.

Uses: Can be crushed to make an aggregate, which helps make concrete more compact.

Where can I see it?: A great place to spot conglomerate is Dunnottar Castle, Stonehaven.

Fun Fact: Closely related to sandstone, displaying similar sedimentary structures.

Rock name: Slate

Rock type: Metamorphic

Description: Slate is a fine-grained, foliated rock.

Formation: Formed through the metamorphism of mud stone or shale.

Uses: Often used for roofing, floors and chalk boards.

Where can I see it?: Simply check out the roofs in your local area to see slate in use!

Fun Fact: The colour of slate can be determined by how much iron it contains.

Rock name: Granite

Rock type: Igneous

Description: Course-grained, intrusive, silica-rich and one of the main components of the Earth’s continental crust. It varies in colour and can be pink to grey.

Formation: Formed below ground over millions of years, allowing the crystals to grow.

Uses: Often used for building walls and as counter tops.

Where can I see it?: You can see many granite buildings in Aberdeen, sometimes referred to as the granite city!

Fun Fact: Some of the oldest igneous rocks in the world are granitic.

Rock name: Sandstone

Rock type: Sedimentary

Description: Mature sedimentary rock, mostly made up of quartz and varying in colour from grey to red.

Formation: Formed when many layers of sand are compressed together over a period of time.

Uses: Used for buildings across Scotland, including the National Museum of Scotland.

Where can I see it?: A great spot to see red sandstone is at the cliffs along the east coast of Scotland, between Arbroath and Auchmithie.

Fun Fact: A lot of new red sandstone in Scotland was formed during the Permian, when it was laid down as giant sand dunes.

Rock name: Marble

Rock type: Metamorphic

Description: A very hard rock that polishes well, is smooth in texture and is often white and green in colour.

Formation: Formed when limestone is heated and compressed (metamorphosed).

Uses: Used for worktops, ornaments, and statues.

Where can I see it?: Iona, the Inner Hebrides.

Fun Fact: Glasgow City Chambers has the largest marble staircase in the world!

Rock name: Limestone, with fossils

Rock type: Sedimentary

Description: A grey, yellow, or white coloured rock, mainly made of calcium carbonate.

Formation: Made from layers of the remains of shells and other sea creatures such as coral.

Uses: Limestone has many uses, including in the construction of buildings and as soil conditioner.

Where can I see it?: You can see limestone at lots of locations across the British Isles, with Malham Cove in England a very famous spot.

Fun Fact: Scottish limestone was once formed when Scotland was positioned in the tropics, closer to the equator.

Rock name: Basalt

Rock type: Igneous

Description: A dark coloured, fine-grained, extrusive rock (igneous rock produced when molten rock cools at or near the Earth’s surface).

Formation: Formed by the quick cooling of runny molten rock from a volcanic eruption, rich in magnesium and iron.

Uses: Used in construction as building blocks and for making cobblestones and statues.

Where can I see it?: There are lots of excellent examples of basalts in Scotland, including Fingal’s Cave and Castle Hill (a basaltic volcanic plug) in Edinburgh.

Fun Fact: When you look at the moon, the dark sections (known as maria) and many of the volcanoes found on Mars and Venus are made of basalt.

Rock name: Gneiss

Rock type: Metamorphic

Description: Stripey, with bands of white/lighter and black/darker material with different compositions.

Formation: Formed when rocks are heated and compressed (metamorphosed) a lot!

Uses: Often used in construction, as flooring, for ornaments and as gravestones.

Where can I see it?: The Lewisian Gneiss (the oldest rocks in the UK at 3 billion years old!) can be found in the North West Highlands of Scotland.

Fun Fact: The oldest rocks in the world (4 billion years old) are gneiss, found in Canada.

Rock name: Diorite

Rock type: Igneous

Description: Speckled white, grey and black rock, with a “salt and pepper” appearance, sometimes described as white granite.

Formation: Formed when a moderately silica-rich, less runny magma cools slowly underground over a long time.

Uses: A base material in the construction of roads, buildings and car parks. It is also used to help control erosion.

Where can I see it?: The Highlands, the Lake District and Snowdonia.

Fun Fact: Diorite was popular among ancient sculptors of the Middle East. The Code of Hammurabi is a black diorite pillar, seven feet tall, inscribed with Babylonian laws in 1750 BC.

Rock name: Coal

Rock type: Sedimentary

Description: An organic sedimentary rock that is black in colour, with a slight sheen. Most types are relatively lightweight.

Formation: Coal is a fossil fuel. Plants and other organic matter die and form layers in swamps and forests. After compression, heating and lots of time, coal forms.

Uses: Coal is burned to generate electricity and is also used in the production of chemicals.

Where can I see it?: Yorkshire, East Scotland (Carboniferous Fife) and Cumbria.

Fun Fact: A third of the US electricity production is sourced from burning coal.

Rock name: Mica schist

Rock type: Metamorphic

Description: Shiny and silvery, with the flat surfaces of mica crystals sparkling in the light.

Formation: Formed when basalt, shale or mudstone are put under great pressure and heat (metamorphosis). The thin flaky mica crystals all align in the same directions (foliation).

Uses: Micas are used in products such as drywalls, paints, and electronics. The mineral is often used in cosmetics to create shimmer.

Where can I see it?: The Highlands, for example Loch Eilt.

Fun Fact: Schist is found in the basement rocks of Mount Everest. The German word for mica is “glimmer”.