Chemical Composition
Definition -
The unit cell of any substance will contain one or and integral multiple of chemical formula units. Mineral formulas are based on the relationship to unit cell volume and the positions of atoms within the unit cell.
Calculation of Chemical Composition
The calculation of the chemical composition is highly straight-forward. The molecular weight from the empirical formula is divided by the sum of the atomic weight of each element to yield the percentage of each element. This is done for each element in the empirical formula and tabulated as the chemical composition. The sort order is based on the electro-negativity of the element.
Additional information provided is the chemical composition expressed as the % oxide of the element. These data are provided to help in the comparison of mineral analyses which use oxide percent. The convention of reporting the oxide percent dates back to when minerals and rocks were analysed using wet-chemical methods to precipitate an element. The precipitate was oxidized under high temperature and the results were weighed as the oxide.
Last Update: 21 Nov 2007