What is a substitution in mineralogy ?
Substitution : mineralogical definition
In mineralogy, this term designates the replacement in a mineral of atoms of one element by atoms of another element.
To occur, the substitution requires several conditions :
- a similarity of atomic radii between replaced atoms and their replacements.
- compensation of electrical loads.
- an appropriate temperature, the possibilities of substitutions generally increasing with the temperature.
Fe and Mg thus commonly replace each other, as do Fe and Mn, Na and K, Si and Al, etc...
This substitution phenomenon leads to the existence of solid solutions, frequent in many groups of minerals : for example in olivines, the magnesium of forsterite (Mg2SiO4) can be replaced in all proportions by iron, leading to fayalite (Fe2SiO4).
To occur, the substitution requires several conditions :
- a similarity of atomic radii between replaced atoms and their replacements.
- compensation of electrical loads.
- an appropriate temperature, the possibilities of substitutions generally increasing with the temperature.
Fe and Mg thus commonly replace each other, as do Fe and Mn, Na and K, Si and Al, etc...
This substitution phenomenon leads to the existence of solid solutions, frequent in many groups of minerals : for example in olivines, the magnesium of forsterite (Mg2SiO4) can be replaced in all proportions by iron, leading to fayalite (Fe2SiO4).
Substitution : gitology definition
In gitology, a substitution deposit is a deposit formed by replacing the initial minerals of the surrounding rocks with recoverable minerals, metallic and/or non-metallic. Substitution deposits appear mainly in a carbonate environment.