Minerals are Earth’s, and other planets, building blocks. Rocks are composed of minerals and the planets are composed of rocks. But what characterizes a mineral? How are they formed? How many minerals are there? Below you’ll find the answers to some of your questions.
Minerals are often chemical compounds, which mean that several elements are bound to each other. Common examples of this are sodium chloride (NaCl), ordinary salt, and silica (SiO2), quartz. There are both minerals that occur naturally in rocks.
A mineral can also composed of more or less pure chemical elements. Examples of this are gold (Au) and diamond (C). Gold is a noble metal, meaning that it often does not react with other elements often to build chemical compounds. It is also resistant to oxidation and corrosion. Gold often occurs in its pure, metallic form, sometimes together with silver or copper.
Minerals normally show a well-arranged inner geometrical atomic structure, called the crystal structure. This means that the elements are composed of symmetrical arrangements in 3 dimensions. We often need to use strong magnification on the mineral to find this crystal structure, or use radiation measurements such as x-rays. However, crystals that have the freedom to crystallize freely often resemble the inner crystal structure on the outside form. One example of this is quartz, which can grow to be large crystals with plane edges if given the right conditions. The amount of surfaces on the crystal, their form and the angles are controlled by the inner crystal structure.
Some minerals, like opal, lack a crystal structure. Opal is a partly organized, hydrated silicate. It often comes in colors like grey, brown, white etc. However, the most famous opals are in a rainbow mix of colors which are considered precious gemstones.
Minerals are formed through geological processes
All minerals are created through geological processes, examples of this are:
- when new rocks are formed through melt (magma) reaching the surface and cooling down to form a volcanic rock,
- when sediments are compacted and transformed to sedimentary rocks deep under the seabed in both inland seas and oceans,
- when existing rocks are metamorphosed, through high pressures and/or temperatures, to new rocks but also
- when hot water circulates in the Earth’s crust and precipitates different elements in the form of minerals (hydrothermal processes).
By geological processes we mean those that happen on our planet. Other planets also show, at least partly, these processes.
Can minerals come from plants or animals, or even human activity?
Materials produced by the plant or animal kingdoms are often called biogenic materials, but due to the fact that these are not crystalline chemical compounds they cannot be classified as minerals. However, these materials may be subject to geological processes, which can turn them into minerals. An example is when dead plants or animals settle on the seabed, gets buried and turn into sedimentary rocks. Another example is when animals and plants that are rich in the element carbon are exposed to different geological processes and transformed to minerals such as graphite and diamonds (pure crystalline carbon with different crystal structures).
Non-crystalline carbon rich geological materials such as peat, oil, pitch, lignite, coal etc. are however not minerals. The popular jewellery material amber is a fossilized resin, and thus also no mineral.
Some substances and compounds that are a result from human activity, for example slag from melting processes, were previously called minerals. But because these compounds have not, yet, been exposed to any geological processes they do not fall into the category of minerals. Thus no materials created from human activity are called minerals.