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Advanced Mineral Concepts: Solid Solution, Phase Diagrams, and Crystal Systems

Figures (10)

Pourbaix diagram of iron.[1] The Y axis corresponds to voltage potential.
Fe–H2O
Cu–H2O
Au–H2O
Al–H2O
Mn–H2O
Zn–H2O–CO32–
A binary phase diagram displaying solid solutions over the full range of relative concentrations
A binary phase diagram showing two solid solutions: α {\displaystyle \alpha } and β {\displaystyle \beta }
The Pourbaix diagram for uranium in a non-complexing aqueous medium (e.g. perchloric acid / sodium hydroxide)[2]

Solid solution is when a mineral can have different elements in its structure, like how olivine can have both magnesium and iron. This means the mineral's chemical formula can vary within a certain range. Phase diagrams show how minerals form under different conditions of temperature and pressure.

They help scientists understand the stability of different minerals. Crystal systems are the basic shapes that minerals can form, like cubes or hexagons, based on how their atoms are arranged. Students should picture these concepts as different ways to describe and understand the structure and formation of minerals.

Solid solution shows how elements can mix in a mineral, phase diagrams show the conditions for mineral formation, and crystal systems show the geometric shapes minerals can take.

Key Points

  • Solid solution refers to the ability of certain elements to substitute for each other within the crystal structure of a mineral, such as the substitution of magnesium and iron in olivine.
  • Plagioclase feldspar is a type of feldspar that forms a solid solution series between albite (sodium-rich) and anorthite (calcium-rich), with intermediate compositions such as oligoclase, andesine, labradorite, and bytownite.
  • Olivine is a silicate mineral that can range in composition from Fe2SiO4 to Mg2SiO4, with the ability of magnesium and iron to substitute for each other within its structure.
  • Calcite is a carbonate mineral with the chemical formula CaCO3, commonly found in sedimentary rocks and known for its reaction with dilute acid to produce carbon dioxide bubbles.

Terms

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