Materials

Firewood is wood that has been collected just to be burnt as fuel. Firewood is usually cut into small pieces so it can fit inside a fireplace.

Foam is made up of a lot of small bubbles, usually found on the top of a liquid like the sea or a glass of beer.
Something that is full of bubbles may also be called foam, such as the foam padding found inside seat cushions.

When an animal or plant dies and is buried under the ground with the right conditions for thousands or even millions of years, it turns to stone. Later when we dig them back up, we call them a fossil. When something has been turned into a fossil it is fossilised.
People have found fossils of all sized creatures, from tiny sea snails, to frogs, right up to enormous dinosaurs. Most of the creatures that people find as fossils are extinct - you can no longer see a living animal of that kind.
The fossil in the picture is a trilobite.

Fuel is something that can be turned into energy. Firewood, coal and gasoline are all fuels that can be burnt to produce fire and heat. Uranium is fuel in a nuclear reactor. Food is fuel for people.

Gasoline, also called petrol in some countries, is a toxic liquid that is used as a fuel in internal combustion engines. Many kinds of vehicle use gasoline to make them run.

A gem, or jewel, is a cut and polished precious or semi-precious stone that can be used to make jewelry.
A gem can also be used to describe something that stands out as being better than everything around it, as in "this figurine is the gem of her collection".

Gold is a heavy, soft, yellow metal that is easy to work with. It is the softest metal, and is very dense, much denser than lead.
Gold is very stable and is used to coat other more reactive metals to protect them, but its primary use is in jewelery. Pure gold is too soft to make jewelery out of, and is usually mixed with silver, copper and other metals.

Graphite is a form of carbon. It has the interesting property of being made up of very thin layers that can be easily rubbed off, so is perfect for drawing with. Graphite is the main ingredient of the "lead" in lead pencils.
Graphite can also conduct electricity, so it has many applications in engineering and electronics.

Grout is a substance made of water, cement and sand that is used to fill up gaps between hard construction materials like tiles. Grout often contains coloring agents, and can be bought in a huge range of colors.

Ice is what happens to water when it is so cold that it freezes. You can see ice as snow in winter. Snow is just tiny bits of ice. In summer, people make their drinks cooler by putting ice in them.