We have modified the Titan-yellow (Clayton-yellow) stain techniques for distinguishing magnesium-rich calcite from other carbonate minerals (Friedman, 1959; Winland, 1971) to make the stain colorfast and permanent. Our modification is a simple fixing procedure which involves dipping the stained thin section or other plane surface in a 5M solution of sodium hydroxide. Fixed in this way, the various chromas (saturations) of red imparted to Mg-calcite will not fade, and the stained thin section can then be covered using standard methods. As Winland (1971) noted, epoxy must be used to cement thin section to glass slide. Chroma of the stain becomes more vivid with increasing Mg content, but a differing rates depending mainly on the crystal or particle size of the constituent; finer constituents such as Mg-calcite micrite cements and pellets generally stain more intensely than coarser ones such as echinoid spines with similar Mg contents.

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