Between a Rock and a Hard Place Quiz

Answer: Igneous

Basalt is an igneous rock, meaning that it is formed when molten magma or lava cools and solidifies. If you're a fan of Led Zeppelin, you might have seen the Giant's Causeway on the cover of 'Houses of the Holy';. It's a World Heritage Site in Northern Ireland made up of multiple columns of basalt, formed millions of years ago by a volcanic fissure.

When basalt cools and contracts vertically, it forms pillars. It is rich in iron and magnesium, and is the most commonly occurring volcanic rock on Earth.

It has also been found on Mars and Venus.

Answer: Igneous

Gabbro is named for a village in Italy, the country where it was first discovered. Similar to basalt, it is rich in iron and magnesium. It is coarse-grained and found in volcanic rock intrusions known as plutons, such as Zuma Rock in Nigeria - an enormous rock bigger than a skyscraper - and the Muskox Intrusion in Canada. Also known as black granite, it is used in the construction industry, albeit on a limited basis because it is difficult to work with.

Answer: Igneous

Obsidian is an igneous rock and a volcanic glass formed from rapidly cooling magma, usually felsic magma containing elements such as silicon or aluminium, which are found in quartz and feldspar. Its most common colour is black, but green, brown and - less commonly - red, orange, blue and yellow versions also exist.

It was heavily used by the Aztecs to make mirrors, and the god Tezcatlipoca was the god of obsidian; other pre-Columbian civilisations used it to make tools, weapons and jewellery. Today, it is still used in jewellery and ornaments, and also used to make scalpel blades, though obsidian blades are more brittle than metal ones.

Answer: Igneous

Pumice is a light, porous igneous rock made from rough volcanic glass, and is formed when highly pressurised hot rock is rapidly ejected from a volcano. The rapid depressurisation and cooling is what gives pumice a foamy appearance; it's also one of the only rocks that can float (as I discovered when playing with my grandma's pumice stone in the bath). Because of its abrasive surface, it is used to exfoliate dry skin and soften hard bits on skin, like corns and calluses.

In ancient Egypt, it was used to remove hair in order to prevent lice, while the ancient Chinese used it in medicine and as nail care.

Answer: Sedimentary

Coal is a sedimentary rock, meaning that it is formed when mineral or organic deposits - often resulting from the erosion of rocks, in the former case - accumulate and are then bonded together in a process called sedimentation. Coal is predominantly made of carbon and is a fossil fuel created from dead plant matter accumulating over millions of years and being converted into coal by a combination of heat and pressure, making it a non-renewable energy source.

It is one of the world's biggest energy sources, with coal mining and production taking off globally during the Industrial Revolution; although some countries have stopped mining coal due to concerns about pollution, others have continued. One lung disease suffered by coal miners is black lung, caused by inhaling coal dust.

Answer: Sedimentary

Shale is a sedimentary rock formed from mud containing clay minerals, and is recognisable by its tendency to split into thin layers, a property known as fissility. It is the world's most common sedimentary rock and is usually grey, though deposits of minerals such as hematite or chlorite may give it a reddish or greenish colour.

It is used as a source for hydrocarbons such as petroleum and natural gas; in the US, the Barnett Shale formation in Texas is a major source of natural gas.

Answer: Sedimentary

Coquina is a sedimentary rock with a very rare property - it's made from fragments of coral and molluscs, trilobites and other tiny creatures with shells. Although some coquinas are looser than others, one property coquinas share is particles that are at least 2 mm in size.

It is usually found in either coastal areas or the former beds of lakes. In Australia and Florida, coquina has been used as a construction material; the Castillo in St Augustine, for instance, is made of coquina. As it is very soft, it has to be left to harden before it can be used for construction.

Answer: Sedimentary

Limestone is a sedimentary rock made from calcium carbonate, which often contains fossils; the English geologist Mary Anning found multiple fossils of sea creatures, such as ichthyosaurs and plesiosaurs, in the limestone deposits at Lyme Regis, Dorset.

It makes up between a fifth and a quarter of the world's sedimentary rock. Limestone is soluble and can be used to create lime when heated. The Rock of Gibraltar is made from limestone, as are the Needles, three stacks of chalk (a type of limestone made from calcite and formed deep underwater) near the Isle of Wight in the UK.

In the Medieval period, it was often used as a construction material because of its hardness and accessibility.

Answer: Metamorphic

Gneiss is a metamorphic rock, meaning that it is formed when a rock formation experiences physical and chemical change as a result of high temperatures and pressures. Gneiss is often recognisable by its light and dark bands (gneissic banding), giving it a striped appearance. If gneiss comes from an igneous rock, such as the Lewisian gneiss of the Hebrides or the ancient Morton gneiss of Minnesota, it is orthogneiss. If it comes from a sedimentary rock, it is paragneiss. Gneiss is mainly used in construction work, such as building asphalt pavements.

Answer: Metamorphic

Schist is a medium-grade metamorphic rock (in that it is subjected to lower temperatures and pressures than gneiss), made from mineral grains that can be split into flakes (a property known as schistosity). Its coarse grains can be seen with a low-power microscope. Types of schist get their names from the minerals they are formed from, such as hornblende schist or talc schist. One of the most common types of schist is formed from mudstone. 'Schist' is also used as a catch-all term for a metamorphic rock when the protolith (the original stone) is unknown.

Answer: Metamorphic

Marble is one of the most well-known metamorphic rocks; if you've ever been to a museum of ancient history, you'll have seen plenty of marble statues. Marble is made from rocks containing carbonate, such as dolomite or limestone, and rarely contains layers.

Although white is the most well-known marble colour, it can also come in black, pink, green, red, grey or banded colours (veins in marble are caused by mineral impurities). As it is harder than limestone, it is used for construction and sculpture; the Taj Mahal, for example, is coated with marble. Because marble is porous, it needs to be cleaned with care.

Answer: Metamorphic

Anthracite is a low-grade metamorphic rock formed from coal. It has a high carbon content and is also known as black coal. The Coal Region of Northeastern Pennsylvania is one of the world's largest deposits of anthracite; the town of Centralia became a ghost town after a vein of anthracite in the local mines caught fire in 1962, and the residents were forced to evacuate when attempts to extinguish the fire failed.

China is the largest global producer of anthracite, and standard grade anthracite is used as a domestic fuel, due to burning with little soot, although it is expensive. The higher the carbon content, the purer the anthracite and the higher the grade.