Materials

Pearls are made inside the shells of mollusks like clams and oysters. They are usually round, and have a soft, translucent glow to them. Pearls have been made into jewellery for thousands of years.

Pebbles are small, rounded stones with no sharp corners. Pebbles are usually made by being worn smooth by water over time, so you most often find them in a river bed or on the beach.

Petrol is another word for gasoline.

Pine is a soft, cheap timber, commonly used for making floors and furniture. It becomes more yellow as it ages.

Plaster is a white powdered substance that is made from gypsum, a kind of stone. When water is added to plaster it stays as a wet paste for a little while but then it goes hard. As it goes hard it gets hot - plaster setting is an exothermic reaction. If you are going to put plaster on your skin you should do it slowly, in thin layers or you could get burnt.
Today, plaster is most commonly used mixed with lime to line the inside walls of houses, or put into bandages to hold a broken bone in place as it heals.

Platinum is a corrosion-resistant precious metal. It is mainly used in jewellery, electronic components and laboratory equipment but it has other uses as varied as the automotive industry and dentistry.

Powder is made when you grind up something into very very small pieces. Powder feels soft to touch. Flour and many spices are a powder, while something like sand is too coarse to be called a powder.

Quartz is the second most common mineral on the surface of the Earth after feldspar. It is made of silicon dioxide in a crystalline structure. Quartz naturally forms colourless six-sided crystals, and is transparent or slightly translucent. Quartz that is milky or is coloured has impurities in it. Quartz that is a pretty colour is usually given a different name, like amethyst.

A rag is a small leftover piece of cloth, usually used for something like cleaning with.
Some people use rags to make things from, like rag dolls or quilts.

A rock is a large, naturally occurring object made of stone. The rock in the picture is jutting out of the ground.