Section 1: Properties of Minerals
A mineral is a naturally occurring, inorganic solid that has a crystal structure and a definite chemical composition. These determine both the physical and chemical properties that are characteristic of each mineral. A mineral must have distinct characteristics in order to be considered a mineral. A mineral must be formed by processes that occur in the natural world. It must be inorganic, meaning that it cannot come from materials that were once part of a living thing. A mineral is a solid, which means it has definite shape and definite volume. A mineral has particles that make it line up in a repeating pattern, which forms a crystal. Finally, it has a definite chemical composition or range of compositions.
Each mineral has certain characteristics that help identify it. Color is used to identify a few minerals that have their own characteristic coloring. Streak is the color of the mineral’s powder, which can be observed by rubbing it on unglazed porcelain. Luster is how light is reflected from a mineral’s surface. Words such as glossy, dull, and metallic are used to describe a mineral’s luster. Each mineral has a characteristic density. Hardness is determined by the Mohs hardness scale, which ranks ten minerals from softest to hardest. Ten minerals were selected as a standard and arranged so that any mineral on the scale would only scratch those below it. The softest is talc and the hardest is diamond.
Each mineral has a unique crystal system where crystals grow atom by atom to form a particular structure. These structures are grouped into six different categories based on the number and angle of the crystal faces. When a crystal breaks, some break easily along flat surfaces. This ability to break is called cleavage. A fracture is when a mineral breaks apart in an irregular way. Some minerals have special properties that can also be used to classify them such as magnetism and ability to grow under an ultraviolet light.