The unit cell of any substance will contain one or integral multiple of chemical formula units (Z value). 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 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.
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 analyzed using wet-chemical methods to precipitate an element. The precipitate was oxidized under high temperature and the results were weighed as the oxide.
Since we have all this detailed chemical composition data, the following search form will identify possible minerals by searching for 1 to 3 chemical analysis. This is a great way to help identify unknown substances.
Other References on Chemical Composition
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Example Subject Searches
The safest way to search for elements is to spell out the element name in full since every page has a chemical composition. Be sure to use sulfur and not sulfate since sulfate is not reported or analyzed. Use chlorine and not chloride, carbon and not carbonate, etc.
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