Minerals are Solid Chemical Substances
A naturally occurring, inorganic (not formed by living organisms), crystalline solid is classed as a mineral.
'Naturally occurring' is important because sugar, ice produced in a freezer, and lab-grown crystals, such as diamonds, are also crystalline solids, but they're not minerals.
Minerals must have a specific chemical composition and an internal crystalline structure. A specific chemical composition means it's composed of specific chemical elements arranged in a defined ratio.
A crystal structure is an arrangement of atoms that comes together in a highly ordered, repeating, symmetrical pattern. This arrangement is known as a crystal lattice. The lattice forms a crystal. If the atoms do not form in this way and are jumbled up, the substance will be amorphous.
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Naturally occurring, non-crystalline solids are known as mineraloids. Examples include amber, which is fossilised tree resin, shungite, opal, pearl, moldavite, which is a tektite, and obsidian, which is a volcanic glass.
Amorphous describes a non-crystalline solid that could be natural or man-made. An example of a man-made non-crystalline solid is glass.
At least 5000 minerals have been identified on Earth, but only about 100 to 150 are common. More than one hundred new minerals are discovered each year.
Most rocks are formed from a small number of the most common 'rock-forming' minerals. Examples include quartz, olivine, calcite and pyroxenes. Peridot is the gemstone variety of olivine. Jadeite is a pyroxene.
Identifying some minerals can be straightforward, but others can be more difficult. Charoite can often be identified on sight alone, but apatite can be far more complex.
The name apatite comes from the Greek for 'deceive' or 'to be misled'.
When identifying a mineral, colour is usually a good place to start. It can also be the most unreliable characteristic because many minerals occur in a range of colours.
Streak and lustre can also help with identification. Streak describes the colour of a mineral in powdered form. It doesn't change and can differ from the visible colour of the mineral.
Lustre describes the way light interacts with the surface of a stone.
The Mohs scale of mineral hardness was created in 1812 as a way of testing the scratch resistance of one mineral against another.
Diamond, which grades 10 out of 10, is the hardest mineral on the scale. Talc, at number 1, is the softest. Corundum, which grades 9, can scratch quartz, which grades 7. Apatite, which is 5, can scratch fluorite, which is 4.
Harder minerals can scratch those which are softer, and those of the same hardness can scratch each other. Hardness is not the same as toughness.
Quartz, feldspar, and mica are three of Earth's most common minerals. Painite, taaffeite, and grandidierite are three of the rarest.
From a nutritional perspective, the word 'mineral' has a slightly different meaning.
Minerals are required in small amounts to enable our bodies to function normally. The amount each person needs differs depending on age, sex, and overall health.
Article Pictures
Our photograph at the top of the page is amethyst. Photograph courtesy of Stan Celestian. The image is clickable and redirects to the original photo.
The second image shows atoms arranged in a crystalline and non-crystalline solid.
Pop-up photos: Diamond - Courtesy of Géry Parent. Corundum - Courtesy of James St.John. Fluorite - Courtesy of Stan Celestian.
The mica is from our collection.
