Overall, the physical properties of minerals provide a reliable means to identify common minerals. However, certain properties can exhibit a range of characteristics or values making them less useful for identification purposes. Choose three physical properties that might vary considerably between samples of the same mineral and explain why such variability might exist.
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1. Overall, the physical properties of minerals provide a reliable means to identify common minerals. However, certain properties can exhibit a range of characteristics or values making them less useful for identification purposes.
Minerals are defined as solid, inorganic substances that occur naturally and have a definite atomic structure and chemical composition. They exhibit several properties that are useful for identification. Color, crystal shape, hardness, and luster are a few of the properties that can be used to determine a mineral's identity. Color is one of the least reliable tests for identifying a mineral sample, but may provide some clues depending on the specimen. Various physical properties, in addition to crystal habit, can be used to identify different minerals. The properties include:
· Luster is the appearance of light reflected from fresh mineral surface, and includes two major subdivisions:
- non-metallic - vitreous (glassy), waxy, pearly, earthy, resinous, etc.
· Cleavage is the tendency to break along the direction of weak atomic bonds and reflects relative strength of bonds within a mineral's atomic structure. Some minerals have cleavage, whereas others do not. Micas provide a good example of the tendency to break along direction of weak atomic bonds. Like all sheet silicates, a single cleavage is well-developed between the sheets. Minerals that do not have cleavage (e.g., quartz) tend to fracture or break irregularly.
Conchoidal fracture is developed where a mineral breaks with smooth curved surfaces (like broken glass). Cleavage may be the best means of identifying between minerals that otherwise look identical, e.g.,
pyroxene ? 90° ...
This solution explains three physical properties that might vary considerably between samples of the same mineral and also explains why such variability might exist.