TREMOLITE VAR. HEXAGONITE CRYSTAL STRUCTURE CHARACTERIZATION BY X-RAY METHODS

The very rare manganese-rich variety of tremolite only found in St. Lawrence Co. New York, commonly known as hexagonite, was originally published in the 1876 Natural Academy of Science volume 28 and discovered by Mr. Goldsmith. This pink to purple amphibole mineral was supposedly a hexagonal form of tremolite but later determined by Dr. George Koenig to be monoclinic.

Since that early publication, only a few studies have been conducted to further characterize the material. This study attempts to characterize the manganese incorporation into the tremolite crystal lattice by three complimentary X-ray techniques, Small Molecule Single Crystal X-ray Diffraction (SCXRD), Wavelength dispersive X-ray fluorescence (WDXRF), and Powder X-ray Diffraction (PXRD).

Two distinct formations (grey fibrous and pink translucent) were crushed, separated under a light microscope and analyzed by WDXRF for variations in elemental composition. Manganese concentrations varied significantly between the grey fibrous grains and pink translucent grains.

A single crystal from each color aliquot was analyzed (SCXRD) to suggest a possible crystal structure for the incorporation of manganese into the tremolite lattice. The three dimensional structures were refined in an attempt to ascertain the amount of partial substitution by manganese.

PXRD data collected from each aliquot was combined with the elemental composition to determine the mineral phase compositions. Finally, the newly suggested model from the SCXRD was refined with Rietveld analysis to achieve an overall characterization for the average crystal composition in each color type.