Viséite is a poorly crystalline mineral which is difficult to study by X-ray diffraction pattern. NMR is a very useful technique to study such poorly crystalline minerals, and 31P, 27Al, and 29Si MAS NMR in conjunction with powder XRD results show that at least our Viséite sample is not a single phase with a structure analogous to that of analcime as previously reported. Rather, it is very disordered with a structure similar to that of crandallite and includes other phases including an undefined aluminophosphate, opal, and a framework aluminosilicate, probably a zeolite. The previously reported variations in the Si content of Viséite are probably due to variable amounts of opal and the framework aluminosilicate.
