Mineral Identification Basics
Minerals are identified by their physical and chemical properties. Key traits include color, streak, luster, density, hardness, cleavage, and crystal form. Each property provides clues to a mineral's identity even before chemical tests are applied.
Color: Tricky Identifier
While color is the most noticeable feature, it's often misleading due to impurities. For example, quartz comes in many colors, but it’s the same mineral, regardless of hue. Reliable identification relies on less variable properties.
Streak: Revealing Powder
A mineral's streak is the color of its powder, obtained by rubbing it on a porcelain plate. Unlike the surface color, the streak doesn't vary with impurities, offering a more consistent identification clue, especially useful for metallic minerals.
Luster: Light Interaction
Luster describes how light interacts with a mineral's surface. Minerals exhibit different lusters like metallic, glassy, pearly, or dull. For instance, galena has a metallic luster, while calcite appears glassy, helping to differentiate between the two.
Hardness: Scratch Test
Hardness is measured on Mohs scale, ranging from 1 (talc) to 10 (diamond). A simple scratch test compares a mineral against common items (fingernail, copper coin) or other minerals to estimate its position on the scale.
Cleavage and Fracture
Cleavage describes how a mineral breaks along specific planes of weakness, resulting in smooth, flat surfaces. Fracture, however, is breakage without cleavage, often resulting in uneven or conchoidal surfaces, like how quartz breaks.
Mineral Identification Kits
Professionals use identification kits containing tools like streak plates, hardness picks, and hand lenses. These kits help in performing tests, combined with knowledge of geologic environments, to accurately identify and study minerals in the field.