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, a mineral, is made of many atoms of the element gold. But minerals can also be chemical compounds, meaning they are made from 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 such 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 qualify. Coal, for example, is a rock but not a mineral. Rocks are inorganic, and coal is not. It’s not made up of identical repeating chemicals — indeed, it recipe can vary depending on what it was made from. So it can’t form a crystal structure. Various minerals may, however, be interspersed within a coal deposit.
In a sentence
Scientists can measure radioactive elements in minerals to find out how much time has passed since that mineral formed.