Mineral (noun, “MIN-er-all”)
Minerals are elements or compounds that, in their solid form, have a crystal structure. Diamonds and table salt are good examples. Minerals occur naturally in the Earth.
They can be made of just one element. A bar of gold, for example, is made of many atoms of the element gold. But minerals can also be chemical compounds. This means they are made two or more elements. Quartz is one example. This mineral is made from one silicon atom and two oxygen atoms. The atoms that make up a mineral form a crystal — a repeating, three-dimensional pattern. People encounter these crystals whenever they pick up a piece of quartz, for example. Or when they put salt on their food.
Most rocks are made of minerals, often several types of minerals smashed together. But not all rocks. Coal, for example, is a rock. But it’s not a mineral. It’s not made up of identical repeating chemicals and the repeating crystal structure of a mineral can’t form.
In a sentence
Scientists can measure radioactive elements in minerals to find out how much time has passed since that mineral formed.