Mineral Properties: Identification and Classification
Classified in Chemistry
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Defining Raya
Raya refers to the color of a mineral when it is pulverized into a fine powder.
Defining Brightness and Its Significance
Brightness
Brightness describes the general appearance of a mineral's cool surface when observed under reflected light. It is influenced by factors such as the refractive index, degree of transparency, and surface polish.
Types of Brightness
Metallic
Minerals with a metallic brightness exhibit a glow similar to polished metals and have a high refractive index.
Non-Metallic
Non-metallic minerals are typically light in color and have a low refractive index. They can be further classified as:
- Silky (resembling silk)
- Pearly (exhibiting a peel-like appearance)
- Earthy (scattering light completely)
- Greasy (having an oily appearance)
- Vitreous (similar to the brightness of glass)
- Resinous (similar to resin)
- Adamantine (reflecting light strongly and brightly, like a diamond)
Luminescence and Its Classes
Luminescence
Luminescence is the property of certain substances to transform visible light into other forms of energy.
Classes of Luminescence
Mechanoluminescence
Produced by mechanical actions such as crushing or rubbing.
Thermoluminescence
Emission of light by a mineral when gently heated.
Fluorescence
Minerals that emit light when exposed to shortwave radiation due to electrons jumping to a higher energy level.
Phosphorescence
Similar to fluorescence, but the process is slower.
Diagnostic Features of Gold
Gold can be identified by its malleability, gold streak, high specific gravity, insolubility in most acids (except aqua regia).
Diagnostic Features of Silver
Silver is characterized by its color, streak, high specific gravity, extreme malleability, and sectility. Conclusive evidence can be obtained by precipitating silver as silver chloride by adding HCl to a solution of silver nitrate.
Factors Affecting Specific Gravity
- The class of atoms composing the mineral
- The way atoms are packed
Factors Involved in Ionic Substitution
Ion Size
The radius of the atom being replaced and the atom replacing it should not differ by more than 15%.
Temperature and Formation
Higher formation temperatures increase thermal disorder, leading to less stringent requirements for substitution in the crystal lattice.
Defining Cleavage
Cleavage occurs when a mineral breaks along planes of low density (weaker bonds), resulting in flat surfaces.
Factors to Consider in Cleavage
- Ease of cleavage
- Degree of perfection of the resulting surface
- Number of cleavage directions
- Crystallographic directions
Classes of Breakage
- Fracture (conchoidal, acicular, splintery, hackly)
- Cleavage
- Parting