Minerals are the fundamental building blocks of all rocks on Earth, and therefore the study of these minerals is the key to understanding the science of Earth. By definition, minerals are “naturally occurring, crystalline solid substances, of inorganic origin, with specific chemical compositions.” Thus, the minerals' characteristics can be as complex as their definition, although most of these characteristics can be classified into several categories.
One of the major categories of mineral characteristics is the minerals' optical properties. Among the optical characteristics of minerals, their color, streak, luster, double refraction, fluorescence and transmission of light are highly important. When it comes to the color of the mineral, most minerals appear opaque, while certain other mineral types mixed with trace minerals can appear translucent to transparent.
However, the streak of the mineral, which is the color of the powdered form of the mineral, is a more reliable characteristic when recognizing minerals of various types. Luster, on the other hand, defines the amount of light reflected by the surface of the hard mineral, and it can range from being metallic to non-metallic or waxy. The degree of transparency is also important when recognizing certain minerals, while the degree of refraction, as in the case of minerals such as calcite, can also be used for mineral identification.
When it comes to the physical characteristics of minerals, the hardness, density, crystal shape and the way the mineral breaks are important. The hardness of a mineral can be measured using the Mohs scale of hardness, in which minerals such as talc are placed lowest in a scale of 1 to 10, while the mineral diamond is placed at the top in the same scale. Crystallization of minerals makes them appear in various sizes and shapes. However, the atoms, molecules and the ions that form the crystal lattice determine the shape of the crystalline mineral.
The crystal lattices are impossible to see with the naked eye and should be viewed through higher magnifications using specialized magnifier lenses. The importance of mineral breakage in its identification is because most crystals will break along lines or smooth surfaces depending on the type of crystal and its lattice structure. In general, mineralogists use two sets of criteria when defining the breakage characteristic of minerals, and these two criteria include the easiness of the cleavage and the direction in which the cleavage takes place.
Given the various chemical structures that give rise to different minerals, scientists have formulated different tests to assess the chemical properties of most such minerals. Acid test and the salty taste are two such tests, and given the wide variations existing in the mineral world, there can be many tests that are used to differentiate between each of these minerals.
In addition to these characteristics, minerals can also show characteristics such as magnetism, water absorption and smell. Therefore, when wanting to recognize a specific mineral, one should look into several different properties rather than relying only on one class of properties or only on a single seemingly significant property.