“…The values for the M1 site in wöhlerite and "marianoite", 0.418 and 0.441 Å respectively, compare with the value found for the Nb site in niocalite (0.372 Å). Clearly lower values have been found for the M2 site in wöhlerite and "marianoite", 0.115 and 0.105 Å, respectively, which compare with the values found at other sites presenting a dominant Zr occupancy in minerals of the cuspidine family: the Zr site in låvenite (with some substitution by Nb): d = 0.214 Å (Mellini 1981); the Zr site in hiortdahlite I: d = 0.176 Å (Merlino & Perchiazzi 1985), in hiortdahlite II: d = 0.092 Å (Merlino & Perchiazzi 1987), and in burpalite, d = 0.035 Å (Merlino et al 1990). …”