|Ferristrunzite crystals from Blaton, Belgium. The imaged zone is about 1 cm wide.|
In 1956 R. Van Tassel (remember the vantasselite story) started a comprehensive study of the Mont-des-Groseillers in Blaton, Belgium. By the construction of the Nimy-Blaton Channel, an interesting geological profile of 25 m thickness was exposed over a length of nearly 1000 m. This whole zone contained a spectacular phosphate paragenesis.
The first mineral he described was crandallite, and lateron a whole list of other minerals followed. One of those was a "manganese-free strunzite". Many years later, in 1983, Peacor et al. described the new mineral and not only confirmed the absence of Mn, but also proved that all the iron present was trivalent, and the X-ray diffraction pattern differed significantly from that of strunzite.
Nowadays the formulae of the three members of the strunzite group are well known :
Ferristrunzite is triclinic, and it could be considered as the oxidation product of ferrostrunzite. It forms aggregates and crusts of light-yellow to brownish prismatic crystals, as well in random orientations as in spherical aggregates. Many crystals are bent or deformed.
Other minerals that occur at the Blaton site are crandallite, minyulite, strengite, phosphosiderite, cacoxenite, beraunite, rockbridgeite, whitmoreite, mitridatite, vivianite, destinezite, allophane/evansite, gypsum and barite. Collectors interested in details can contact me by e-mail : I have plenty of literature and other data. In 1990 we discovered really by accident a second Belgian occurrence of ferristrunzite in Haut-le-Wastia, Anhée, Namur Province, Belgium. This locality is about 80 km from Blaton.
|Ferristrunzite crystals from Blaton, Belgium. See scale bar on the image.|