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The tricky bits ... atoms, molecules and the rest

There are around four thousand different minerals in the world. They are all naturally occurring inorganic solids. Each mineral is defined by its particular chemical composition and crystal structure. To explain what a mineral is properly, we have to introduce you to a bit of chemistry.

Minerals are made up of chemical elements. A chemical element is a substance that is made up of only one kind of atom. Have you heard of oxygen, hydrogen, iron, aluminium, gold and copper? These are all chemical elements.

But what is an atom?

An atom is the smallest unit of any chemical element. They are the building blocks that make up each chemical element, and are far too small to see with the naked eye. Imagine a small piece of copper, for example. Even the tiniest piece of copper is made up of billions and billions of copper atoms.

There are 103 types of atoms, and because each chemical element is made up of only one kind of atom there are 103 chemical elements.

Copper atoms stack together to form a piece of copper

Billions and billions of copper atoms stack together to form a piece of copper

Each mineral has a fixed chemical composition. Some minerals are made up of just one chemical element - they contain only one type of atom. Native copper is made up of copper atoms only. Most minerals are chemical compounds - they contain atoms of more than one chemical element

So what is a chemical compound?

Put it this way. Just as chemical elements are made up of atoms, a chemical compound is made up of molecules. Each molecule in a chemical compound is made up of two or more different atoms connected together.

Halite is a chemical compound. It is also called sodium chloride, but you would probably know halite better as rock salt - yes, the kind you put on your fish and chips. Each molecule of halite contains one atom of an element called sodium connected to one atom of an element called chlorine. Halite always contains just as many sodium atoms as it does chlorine atoms: this 'formula' does not vary - halite, like all other minerals has a definite chemical composition.

Atoms of chlorine and sodium       Molecules of halite
Chlorine and sodium atoms will connect together to make halite molecules

The atoms in a mineral are arranged in an organised 'atomic structure'. They connect together to form molecules, and the molecules stack together in a regular pattern to form a crystal. The shape of a crystal depends on the way the molecules are stacked up inside it.

There is a set way in which the sodium atoms "connect" to the chlorine atoms to make a halite molecule, and these molecules can stack together to form a halite crystal.

Halite molecules together to form a halite crystal       Halite crystals or rock salt
Halite molecules stack together to form halite crystals - this is the salt we eat everyday

All the properties of a mineral - its crystal shape, hardness, colour, lustre - depend on which chemical elements it is made of and how the atoms of these elements are arranged inside it.

Now you really ought to know what a mineral is, so why not try our Quiz to test yourself.

Still confused? If you read these pages and complete the quiz, you should have a pretty good idea of what a mineral is.

Defining a mineral
Why is a mineral like a cake?
The tricky bits ... atoms, molecules and the rest
What is a mineral? The quiz!