What are the characteristics of minerals?

The physical characteristics of minerals include traits which are used to identify and describe mineral species. These traits include color, streak, luster, density, hardness, cleavage, fracture, tenacity, and crystal habit. Certain wavelengths of light are reflected by the atoms of a mineral's crystal lattice while others are absorbed. Those wavelengths of light which are reflected are perceived by the viewer to possess the property of color. Some minerals derive their color from the presence of a particular element within the crystal lattice. The presence of such an element can determine which wavelengths of light are reflected and which are absorbed. This type of coloration in minerals is termed idiochromatism; different samples of an idiochromatic mineral species will all display the same color. Other minerals are colored by the presence of certain elements in mixture. Different samples of such a species may exhibit a range of similar colors. Still other mineral species may usually be colorless, but may display several different and startling colors when trace amounts of impurities, or elements which are not an integral part of the crystalline lattice, are present. Coloration which is caused by the presence of an element foreign to the crystal lattice, whether in mixture or in trace amounts, is termed allochromatism. Certain elements are strong pigmenting agents and may lend vivid colors to specimens when they are present, whether as a part of the crystal lattice, in mixture, or as an impurity. These elements are termed the chromophores. Streak is the color which a mineral displays when it has been ground to a fine powder. Trace amounts of impurities do not tend to affect the streak of a mineral, so this characteristic is usually more predictable than color. Two different specimens of the same species may be expected to possess the same streak, whereas they may display different colors.