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.
The calculation of the chemical composition is straight-forward. The molecular weight from the empirical formula divided by the sums of the atomic weights 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. Please note the sort order is based on the electro-negativity of the element.
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