Minerals are fundamental components of Earth, forming rocks, sands, and soils. A strict scientific definition distinguishes true minerals from other substances, allowing geologists to consistently identify and classify them.
What Makes Something a Mineral?
A mineral is a naturally occurring, inorganic solid with a specific chemical composition and an orderly internal atomic structure. These precise criteria provide a framework for scientific classification, enabling accurate identification and study of Earth’s minerals.
The Five Defining Characteristics
Minerals must meet five specific characteristics to be classified as such, each contributing to their unique identity.
A mineral must first be naturally occurring, meaning it forms through geological processes without human intervention. For example, synthetic diamonds are not considered minerals because they are man-made, despite being chemically and structurally identical to natural diamonds.
Second, a mineral must be inorganic, meaning it is not formed from living organisms or organic processes. Substances like coal (derived from plant matter), pearls, and amber (from biological activity) are therefore not classified as minerals.
Third, a mineral must be a solid at normal temperatures found on Earth’s surface. This excludes liquids like water and gases from being classified as minerals, though ice (solid water) meets all other criteria and is considered a mineral.
Fourth, each mineral possesses a definite chemical composition, meaning it has a specific chemical formula that is consistent. For instance, quartz always has the chemical formula SiO2, composed of silicon and oxygen atoms in a fixed ratio.
Finally, a mineral must have an orderly atomic structure, also known as a crystalline structure. This means its atoms are arranged in a precise, repeating three-dimensional pattern, which influences their physical properties. For example, halite (table salt) forms cubic crystals due to the orderly arrangement of its sodium and chlorine atoms, while quartz often forms hexagonal crystals.
Why These Criteria Matter
These strict definitions are fundamental for geologists and other scientists. They provide a standardized way to accurately classify and identify minerals, facilitating precise communication and research. This classification system helps distinguish true minerals from rocks (aggregates of minerals) or synthetic materials. By adhering to these criteria, scientists can better understand Earth’s geological processes, identify valuable resources, and conduct research on Earth’s composition and history.