Convert to oxide percent


Results from geochemical analyses are often in weight percent (sometimes in ppm for trace elements).  Sometimes, to compare your numbers to others in the literature, you will need the elements expressed as oxides, e.g. % MgO instead of % Mg.


To figure this out, remember that your weight percent is the number of grams of your element per 100 g of sample.  Thus if you multiply by grams oxide per gram of the element, you will be left with g oxide per 100 g sample, the number you want.

For example, take MgO.  Imagine that your sample has 5% Mg.  To convert to % MgO, calculate:

5 x (24.305 + 15.994)/24.305

= 8.29 % MgO

In the calculation above, 24.305 is the atomic mass of Mg and 15.994 is the atomic mass of O.