Abstract

An occurrence of rare particles of the multiple oxide tapiolite in beach sands near Otorokua Point, southern Westland, New Zealand, is recorded. For this mineral the following data have been determined: ONa = 2.33 ± 0.01, ENa = 2.53 ± 0.04. E – O = 0.20. O = pale brown, E = reddish-brown to opaque. E > O. S.G.21°C. = 7.65. X-ray diffraction powder patterns show that the mineral has a true trirutile structure with unit cell dimensions of a0 = 4.750 Å, c0 = 9.208 Å, and with d-spacings and intensities that are comparable to those recorded for analyzed tapiolite from Brazil and Morocco, but distinct from the pattern yielded by unheated tapiolite from Skogsbole, Finland. The latter occurrence is shown to have a rutile structure but, after appropriate heat-treatment, a trirutile structure is developed with resultant denser packing of the atoms. Unit cell dimensions for ordered and disordered Skogsbole tapiolite, determined from quartz-calibrated Weissenberg films, are a0 = 4.752 Å, c0 = 9.204 Å, and a0 = 4.753 Å, and c0 = 3.092 Å respectively.

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