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International Union of Crystallography “International Tables for X-ray Crystallography” Vol. I: Symmetry Groups. Henry N. F. M. and Lonsdale K. (eds.) Birmingham, England, Kynoch Press. pp.15 - 21. 1969

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• TITLE: Investigation Of Hardness Anisotropy In Tourmaline

  AUTHORS: M.O. Adeoye, O.O. Adewoye

  KEYWORDS: Tourmaline, Hardness anisotropy, Microhardness, Knoop

  JOURNAL NAME: Journal of Minerals and Materials Characterization and Engineering, Vol.3 No.2, October 20, 2004

  ABSTRACT: Tourmaline is a ring silicate material with a hexagonal crystal structure. Tourmaline crystal is made use of as an electronic component, e.g, as a transducer, mainly because of the anisotropy it exhibits in its properties. Microindentation technique was employed in the research reported in this paper, using a Knoop indenter, to investigate the anisotropy in the hardness of the tourmaline crystal on its two major crystallographic planes: (0001) and {10 10}. The material was found to exhibit hardness anisotropy in conformity with its rotary symmetry elements. The material was identified and analysed using various x-ray techniques, and was found to contain some impurities as expected of natural crystals. Tourmaline was found to have a Si/Al ratio of 1.4. The orientations of the crystal samples were determined by obtaining and indexing the Laue x-ray back-reflection patterns of the crystal samples.