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Complete Solid Solution occurs when two elements can substitue for each other completely in a mineral. Olivines are excellent examples of this type of solid solution. Forsterite, Mg2SiO4, and fayalite, Fe2SiO4, have identical structures because the ions Mg2+ andFe2+ are very nearly the same size and are chemically similar. If both iron and magnesium are present in the environment of crystallization, a single mineral with a compostion intermediate between forsterite and fayalite will form. This mineral is considered to be a "solution" of fayalite and forsterite. Because minerals with all possible intermediate compositions can be formed, the formula is written (Mg,Fe)2SiO4, and the general name, regardless of Mg:Fe ratio is olivine.
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The olivines are referred to as members of a complete solid solution series between the Magnetium (Mg) end member called forsterite, and the Iron (Fe) end member called fayalite. Mg-rich olivines are light green, and Fe-rich olivines are dark green or black. Olivines with intermediate compositions are intermediate in color. Their other physical characteristics also vary between those of the end members. In such minerals either pure end member is seldom found, though they may be synthesized in the laboratory.
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Complete Solid Solution occurs when two elements can substitue for each other completely in a mineral. Olivines are excellent examples of this type of solid solution. Forsterite, Mg2SiO4, and fayalite, Fe2SiO4, have identical structures because the ions Mg2+ andFe2+ are very nearly the same size and are chemically similar. If both iron and magnesium are present in the environment of crystallization, a single mineral with a compostion intermediate between forsterite and fayalite will form. This mineral is considered to be a "solution" of fayalite and forsterite. Because minerals with all possible intermediate compositions can be formed, the formula is written (Mg,Fe)2SiO4, and the general name, regardless of Mg:Fe ratio is olivine.
The olivines are referred to as members of a complete solid solution series between the Magnetium (Mg) end member called forsterite, and the Iron (Fe) end member called fayalite. Mg-rich olivines are light green, and Fe-rich olivines are dark green or black. Olivines with intermediate compositions are intermediate in color. Their other physical characteristics also vary between those of the end members. In such minerals either pure end member is seldom found, though they may be synthesized in the laboratory.
Go to a listing of Rocks by mineral group
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Go to a listing of Rocks by mineral group
