What counts as a mineral
A mineral is a natural, solid, non-living (inorganic) substance with a crystal structure and a definite chemical composition. Examples are sulphur (an element), hematite (iron oxide, red, widespread in Egypt’s Eastern Desert), quartz, halite (rock salt, sodium chloride), mica, talc and galena. We describe minerals by their properties. Colour: sulphur is yellow; quartz can be violet or pink because of impurities, so colour alone can mislead. Lustre: galena is shiny like metal; ancient Egyptians ground it to make kohl, but we mention it only as history because it contains lead and is toxic. Transparency: talc is opaque, mica is translucent, and pure quartz is transparent. Opal is called a mineraloid because it is not crystalline. Not everything shiny is a mineral: metals made by people are not. Coal and oil are fossil fuels, made from living things, so they are not minerals. Water in the liquid state is not a mineral, but ice is. Sugar is crystalline but is made by plants, so it is not a mineral. Quartz is silicon dioxide and not “pure silicon”.
| Mineral | Property | Note |
|---|---|---|
| sulphur | yellow | an element |
| galena | metallic lustre | contains lead: toxic |
| talc | opaque | very soft |
| mica | translucent | splits in sheets |
| quartz | transparent when pure | colour varies |
Mineral or not? Sort ten household items into mineral or not: table salt, sugar, a pencil lead (graphite), a steel spoon, a lump of coal, a glass of water, an ice cube, a piece of sandstone, a plastic cup, a copper wire (note: copper wire is made by people). Give one reason for each. Press a pencil lead on paper and describe its shine. Do not scratch things with a knife or glass.