Definition
The format for the chemical formula is based on the reported formula from the literature source for the mineral. In many cases, the formula is base on the structural interpretation of the mineral, especially the silicates.
The chemical formula is closely matched to the mineral's crystallographic unit cell dimensions and "Z" value.
Special symbols are used where a hole (vacancy) is present in the formula. For this database, the "[ ]" square brackets are used to signify this vacancy.
e.g.: ([ ],Fe,Mg)(Mg,Al,Fe)5Al4Si2(Si,Al)2(B,Si,Al)(O,OH,F)22
Rare Earth Elements in mineral formulae are denoted by the symbol REE .
e.g.: (Na3(Ca,REE,Sr)3(CO3)5)