Opmerkingen over ontstaan en structuur van vivianiet en metavivianiet

In this article some special features of vivianite are briefly described mainly with reference to its structure. In The Netherlands vivianite (made up of iron, phosphate and water) commonly occurs as concretions. When exposed to the air (oxygen) its outer surface rapidly oxidizes: Fe+2 -> Fe+3, with a concomitant change in colour, from white (unoxidized) to blue (oxidized). Adding OH- during oxidation results in the collapse of the monoclinic crystal structure and a change into triclinic symmetry. This triclinic phase is called metavivianite. A brief survey of matrices in which vivianite genesis can take place (usually unconsolidated sediments) is added. It is even known from very old (e.g. Palaeozoic) rocks; its genesis, however, is always secondary and relatively recent.