Solid solution

As a solid solution (MK) or a crystal is called crystallite, which consists of at least two different chemical elements, wherein the foreign atoms or ions are randomly distributed. These can be either in the interstitial sites be incorporated ( solid solution or interstitial solution) or an atom of another element replaced by substitution (substitution solid solution ). Mixed crystals are thus solid solutions, which, if they have metallic properties are also known as alloys.

Mixed crystal formation

There are two types of mixed crystal formation:

• In homöotypen mixed crystal formation, the substances involved have the same crystal system, which consequently also has the solid solution; Compare this to binary systems with complete solid solubility.
• In the heterotypic mixed crystal formation, however, one of the substances involved forcing the / the other when installing on its crystal structure. Compare this two-component systems with limited solubility in the solid state.
• If the atoms of the elements involved are no longer statistically randomly distributed in the lattice, one speaks of intermediaries crystals or intermetallic compounds whose crystal system does not correspond to the basic elements.

Mixed crystals in minerals

In the realm of minerals mixed crystals rarely go from pure substances, but mostly from chemical compounds. Two minerals defined composition here form a so-called solid solution series (for short: mixed batch ) whose end members they represent and their mixed crystals are often given names that do not allow conclusions as to their composition.

Thus, for example, labradorite, a mixed crystal series albite - anorthite, with 50-70 % of anorthite.

The minerals forsterite ( Mg2SiO4 ) and fayalite ( Fe2SiO4 ) form a complete solid solution series, the olivine series ( [ Mg, Fe] 2SiO4 ). Other examples are the biotite series between phlogopite and Annite and the melilite series between Akermannit and gehlenite.

Some solid-solution series contain miscibility gaps. This means that in certain circumstances the two end members, two phases exist. An example is the number of plagioclase albite anorthite. Many rows are completely mixed crystal at a high temperature, but have such low temperature miscibility gaps. Some crystals can dissolve small amounts of other elements. This is known as Diadochie. An example is the incorporation of magnesium into calcite (CaCO3). Here there is no complete miscibility for dolomite ( CaMg ( CO3) 2 ) or magnesite ( MgCO3 ).