Formula Weight Calculation

Calculating the formula weight for a given mineral or dissolved constituent is a common task when working with hydrochemical data. The Formula Weight Calculator allows you to select a predefined mineral or enter a formula manually. Fontus calculates the corresponding formula weight automatically after every change in the form. The coefficients for elements in the formula must be whole numbers. Minerals such as Na.96Al.96Si2.04O6:H2O (Analcime) will not be calculated correctly.

The notation for hydrous minerals containing water in their structure uses a dot to separate the mineral from the water molecule. For example, the gypsum formula must be written as CaSO4.2(H2O), the notation CaSO4:2(H2O) or CaSO4·2(H2O). Also, ensure that if the numeric factor in the formula relates to more than just the next element, the group of elements to be multiplied by the coefficient must be embraced by parentheses. For example, writing gypsum as CaSO4.2H2O would give a wrong result since only hydrogen is multiplied by a factor of two. In contrast, in the formula written as CaSO4.2(H2O) the entire water molecule is multiplied.

Below the formula weight calculation output field, the formula elements are shown with their element-molal weight, amount of mols, total weight, and weight percent.

The figure below shows the example for the calculation of Calcite (CaCO₃).

In the bottom section of the form, Fontus displays an expander widget, including a list of the periodic system, specifying the name, symbol, and atomic mass for all elements. All elements include hyperlinks to their page on wikipedia.