Mineral

A mineral is a naturally occurring solid substance with a specific chemical composition and an ordered internal structure.

In geology and mineralogy, the definition of a mineral is quite precise. To be classified as a mineral species, a substance must be formed by natural geological processes. These processes can happen on Earth or on other extraterrestrial bodies. This definition excludes substances made entirely by humans, which are called anthropogenic. It also generally excludes substances made by living organisms, known as biogenic. However, some exceptions exist where geological processes are involved in the creation of biogenic materials.

Every mineral must possess a well-defined crystallographic structure. This means the atoms inside are arranged in a specific, repeating pattern. This internal order determines many of the physical properties we see. For example, it influences how a mineral breaks, which is called cleavage.

It also affects the hardness of the substance. Scientists use the Mohs scale to measure this relative hardness.

If a natural solid lacks this organized atomic arrangement, it is called a mineraloid. Common examples of mineraloids include obsidian and opal. These substances are natural but do not have the required crystal structure.

Chemical composition is another essential requirement for a mineral. Most minerals have a fairly fixed recipe of chemical elements. However, some minerals can have variable compositions through a process called solid solution. This happens when different elements occupy the same positions in the crystal structure.

For instance, the mineral mackinawite can have varying amounts of iron and nickel. In some cases, these variations are so large that scientists split them into a mineral group. The olivine group is a famous example of this. It includes minerals like forsterite and fayalite, which differ based on their magnesium and iron levels. Even when the chemistry changes slightly, the underlying structure remains the same.

Sometimes, a single chemical compound can form different minerals. This occurs if the atoms arrange themselves into different crystal structures. For example, silicon dioxide can form quartz or stishovite. Even though they are made of the same elements, they are considered different mineral species. This is because their internal patterns are unique. The International Mineralogical Association, or IMA, is the body that manages these definitions. They are responsible for the nomenclature, or naming system, of all mineral species. Currently, the IMA recognizes 6,145 official mineral species.

Mineral names often follow specific patterns. Most names end with the suffix "-ite." However, some older names like diamond or galena do not follow this rule. Names are often derived from the person who discovered them or the location where they were found. Other names come from the mineral's chemical makeup or its physical appearance. Scientists classify these vast numbers of minerals using systems like the Dana or Strunz classifications. These systems group minerals by their key chemical constituents. This helps researchers organize the incredible diversity of the natural world.

There are many different chemical groups of minerals. Silicate minerals are the most abundant, making up about 90% of the Earth's crust.

Other important groups include native elements, which consist of a single pure element. There are also sulfides, such as galena, and oxides, such as quartz. Other categories include halides like rock salt, carbonates like calcite, and sulfates like gypsum. Each group is defined by the specific elements that combine to form the mineral. Understanding these groups helps geologists identify what the Earth is made of.

It is important to distinguish minerals from rocks. A rock is a bulk solid material that is relatively homogeneous at a large scale. A rock is often an aggregate, or a collection, of many different minerals.

Some rocks are made of just one mineral, such as limestone, which is mostly calcite. Other rocks, like granite, are defined by the proportions of several minerals like quartz and feldspar. Some rocks are even composed of non-mineral material, such as coal, which comes from organic carbon. In a rock, the most common minerals are called rock-forming minerals. These are the essential building blocks of the Earth's surface.