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2. G.E. Christidis, editor, in Advances in the Characterization of Industrial Minerals (Mineralogical Society of Great Britain and Ireland, 2011), p. 1.
3. D. Eisenhour and F. Reisch, in Industrial minerals & rocks: Commodities, markets, and uses, edited by J.E. Kogel, N.C. Trivedi, J.M. Barker and S.T. Krukowski, 7th ed. (Society for Mining, Metallurgy, and Exploration, 2006), p. 371.
4. Ministry of Trade, Republic of Turkey. https://www.trade.gov.tr/data/5b8fd5bf13b8761f041fee9b/Mining.pdf.