Rock Me! Trivia Quiz

Sandstone is formed when grains of sand are compressed, and bind together to form a rock. You can usually see the sandy texture, and there are often different layers, as different kinds of sand settle in the same place. This particular sample came from a region that had an earthquake sometime after the rock had solidified, as you can tell by the way the layers do not line up.

This is called a fault: the segment on the left is now higher than the one on the right, but just looking at this we cannot tell which one moved.

Coal is formed when the remains of plants decay underwater, leaving behind lots of carbon which then hardens into a rock. There are often a number of other chemicals along with the carbon, such as sulfur, which is released as pollution when the coal is burned for energy. Coal use has increased dramatically since the Industrial Revolution began in the 19th century.

Not only is it used as a source of energy, but it is also a key ingredient in making high quality steel. Burning coal to produce energy (which is often then used to produce electricity) means large amounts of carbon dioxide are released, which has led to an increase in the temperature of the earth's atmosphere, and the need to find alternative energy sources for the future.

Limestone is a white or light grey rock made up primarily of calcium carbonate, formed either from the skeletons of animals which decompose and then settle to form a rock or from water carrying the calcium carbonate deposits some of the mineral. Chalk is a soft form of limestone, found not only in classrooms through the 20th century but also visible in formations such as the White Cliffs of Dover.

When the rocks in an area are limestone, some of it may dissolve when water passes through it, forming caves under a limestone surface. Then more rain filtering down can pick up some of the calcium carbonate in the surface rock; when that liquid emerges into the cave, the change of environment may make it deposit the mineral again. Over time, this process can result in the formations shown in the photo. The rocks hanging from the ceiling (formed in the same way that icicles form on the edge of a roof during winter in places where winter temperatures are below freezing) are called stalactites. the ones on the ground, formed as drops of water hit the floor before depositing the calcium carbonate, are called stalagmites.

Marble is called a metamorphic rock, meaning it is formed when high heat and pressure are applied to another kind of rock, making it change its texture. When the sedimentary rock limestone is subjected to these conditions it is changed into marble. If the limestone is very pure, the marble will be a pure white colour; marble that is formed from other minerals that contain calcium carbonate as one of their components will be coloured, often pink or green.

Marble is highly valued for use by sculptors to make statues, and may be used by architects to create a stunning outer surface on their buildings.

Shale is similar to sandstone, but is made from smaller particles so it lacks the grainy appearance of sandstone, and is sometimes called mudstone or claystone to describe the smaller particles that have settled to form it. Shale, more precisely, is mudstone or claystone which has formed so that it easily splits into layers.

Sometimes, as shale forms, pockets of natural gas are trapped between the layers. During the end of the 20th century techniques were developed to extract this gas, called fracking. Since the shale has layers that trap the gas, it is not as simple as drilling a hole to let it out, as can be done for the gas associated with a coal seam. Fracking makes the gas available, but can have serious consequences for the surrounding environment.

Slate is a metamorphic rock formed when shale is exposed to a lot of heat and pressure. Like shale, it forms in layers, but it is much harder. Slate has been used to make tiles for the roofs of buildings, and as a floor covering.

For many years a sheet of slate was commonly used for temporary writing, usually with chalk. Through at least the middle of the 20th century, a blackboard made of slate was found in most classrooms, and they are still found in places where the modern high-technology classroom display tools are not available. A smaller piece of slate, often in some kind of wood frame, was designed for individual use. The expression 'wiping the slate clean', which means having a chance to start something over, arises from the actual process of removing what has been written on a slate.

Granite is an intrusive igneous rock, meaning it forms underground as magma cools. As you can see from the picture, it contains a mixture of different minerals with varying colours, but usually includes quartz and feldspar. The bits of these minerals are relatively large, leading to the visible mottling which is characteristic of granite.

Its durability when exposed to the weather has made it a popular building material for thousands of years, and it is also commonly used for grave headstones.

Basalt, like granite, is formed when magma cools inside the earth. It is made of much smaller grains, because the magma forming it cools quite quickly. Its minerals are a mixture, but they are low in quartz and feldspar, and higher in one or more minerals in a group called tectosilicates, leading to its typical dark grey colour.

The photo shows a famous Irish formation of basalt rocks which have cooled to form columns with polygonal tops. Most of them are hexagons, with six sides, but some have a different number of sides. They look like stepping stones, and are called the Giants Causeway. According to legend, they were formed when the giant Finn MacCool built the causeway so he could fight a Scottish giant. Following his victory, the Scottish giant ran home, destroying most of the causeway as he ran. Only this bit on the shore of Northern Ireland and another on a Scottish island remain.

Obsidian is sometimes called volcanic glass, because of its smooth and shiny surface. It forms when lava from a volcano cools so rapidly that no crystals have time to form, leaving a hard rock which fractures to form sharp edges. These edges were used by early people to produce tools, both knives and spearheads. Its shiny surface also led to its use as a mirror and in jewelry.

Pumice, often called the rock that floats, is formed (like obsidian) when lava cools so quickly that no mineral crystals form. What makes pumice special is the way that pockets of air get trapped as it cools. This happens because it is thrown into the air during an eruption, and the change in pressure around it means that materials such as water and carbon dioxide which are dissolved in the lava are changed into a gas.

These bubbles give pumice a rough surface, which makes it useful as an abrasive (something that scours and polishes). It has been used over time (either as a piece of rock or ground to a powder) to remove unwanted hair, to groom nails, as a toothpaste, to exfoliate skin, and to remove calluses.