MEIERANITE, Na2Sr3MgSi6O17, A NEW MINERAL FROM THE WESSELS MINE, KALAHARI MANGANESE FIELDS, SOUTH AFRICA

摘要

A new mineral species, meieranite, ideally Na2Sr3MgSi6O17, has been found in the Wessels mine, Kalahari Manganese Fields. Northern Cape Province, South Africa. It occurs in isolated aggregates embedded in a matrix mainly of sugilite, along with minor aegirine and pectolite. Crystals of meieranite are up to 0.5 x 0.5 x 0.4 mm in size. No twinning is observed. The mineral is light blue to blue in transmitted and under incident lights, transparent with white streak, and has vitreous luster. It is brittle and has a Mohs hardness of 5.5; cleavage is good on {010} and no parting was observed. The measured and calculated densities are 3.41(3) and 3.410 g/cm(3), respectively. Optically, meieranite is biaxial (-), with alpha = 1.610(1), beta = 1.623(1), gamma = 1.630(1) (white light), 2V (meas.) = 70(1)degrees, 2V (calc.) = 72 degrees. The calculated compatibility index based on the empirical formula is -0.007 (superior). An electron microprobe analysis yields an empirical formula (based on 17 0 apfu) of Na-1.96(Sr2.91Ba0.03Ca0.03Pb0.02)(Sigma 2.99)(Mg0.62Mn0.28Co0.07Fe0.01)Sigma 0.98Si6.03O17, which can be simplified to Na2Sr3MgSi6O17.