Minerals provide raw materials for industry and are found in rock formations found throughout our homes, cities and parks. Furthermore, minerals form soils which support agriculture as well as aquifers that supply us with water.
Certain properties used to identify minerals include luster, cleavage and specific gravity; while less obvious features can also help.
Physical Properties
Minerals can be classified according to their physical properties – color, crystal form (or shape), hardness, luster, density and cleavage or fracture. An ideal physical property would provide a clear and unambiguous result for each mineral – like how running nose or sore throat might help diagnose an illness.
Cleavage refers to a mineral’s ability to break apart into flat surfaces. Some minerals, like calcite, possess perfect cleavage while others may only possess poor cleavage. Cleavage can help identify minerals even when museum specimens or book pictures show various shapes and arrangements of crystal faces.
Luster refers to the sheen or brilliance exhibited by certain minerals such as micas and talc, such as willemite or green willemite from Franklin Mine in New Jersey in this photograph. Some minerals can reflect light; this green willemite example from Franklin Mine can reflect it brilliantly while other types emit visible light when energy with wavelengths shorter than visible light is present.
Chemical Properties
Numerous mineral properties rely on the strength of bonds between atoms in crystals. While their crystal structures might change with age, their characteristics rarely do. Mineralogists use property differences between minerals to identify them according to standards established by their discoverers or by the Commission on New Minerals and Mineral Names.
Cleavage planes provide us with an invaluable means of distinguishing similar-appearing minerals, and their direction and angle provide information about their crystal structures. Cleavage also gives us clues as to their composition of elements arranged within their mineral crystal structures.
Some minerals, like talc and chlorite, are flexible due to weak van der Waals and hydrogen bonds that allow slippage between layers when pressure is applied; other minerals, like pyrite and chalcopyrite are rigid due to strong covalent bonds tying their layers together tightly. Many minerals also possess unique lusters or streaks which aid identification.
Optical Properties
Light passing through most nonopaque minerals vibrates or excite atoms within them, slowing its velocity of wave. If polarized light enters a mineral with long dimensions and well-developed cleavage, however, it may make waves vibrate in two distinct directions simultaneously: length fast (faster) and length slow (slower), which we refer to as birefringence.
Minerals exhibit many distinct optical properties. For instance, certain minerals show interference colors (isochroism) at lower magnifications that appear as bright bands encasing dark backgrounds, while others fluoresce under UV lighting.
Thin section images of minerals with good cleavage and crystal structures reveal parallel planes, known as cleavage planes, in thin section views of these mineral specimens, providing invaluable clues as to their identity.
Economical Properties
Minerals have made the modern world more accessible, enabling people to build cities and economies reliant on mining ores. We mine metals like gold and copper as well as nonmetallics like asbestos and silica sand; in addition, some igneous and sedimentary rocks such as halite and sylvite may also be mined for their chemical compositions such as halite.
Geologists consider certain minerals so integral to our economy that geologists consider them “critical”, seeking ways to increase domestic production to lessen our reliance on foreign supplies and prevent disruptions to domestic supplies. President Trump recently signed an Executive Order to improve America’s ability to locate domestic sources for critical minerals while encouraging companies to explore opportunities for increased production and export of these essential materials.
Minerals can be considered economically viable when they can be extracted and produced profitably. Geologists evaluate a mineral deposit’s size, concentration of ore minerals and economic viability before deciding if mining it makes economic sense.
