MINERALS CAN BE IDENTIFIED BY STUDYING features such as fracture, cleavage, crystal system, habit, hardness, color, and streak. Minerals can break in different ways. If a mineral breaks in an irregular way, leaving rough surfaces, it possesses fracture. If a mineral breaks along well-defined
planes of weakness, it possesses cleavage. Specific minerals have distinctive patterns of cleavage; for example, mica cleaves along one plane. Most minerals form crystals, which can be categorized into crystal systems according to their symmetry and number of faces. Within each system, several different but related forms of crystal are possible; for example, a cubic crystal can have six, eight, or 12 sides. A mineral’s habit is the typical form taken by an aggregate of its crystals. Examples of habit include botryoidal (like a bunch of grapes) and massive (no definite form). The relative hardness of a mineral may be assessed by testing its resistance to scratching. This property is usually measured
using Mohs scale, which increases in hardness from 1 (talc) to 10 (diamond). The color of a mineral is not a dependable guide to its identity as some minerals have a range of colors. Streak (the color the powdered mineral makes when rubbed across an unglazed tile) is a more reliable indicator.
