This is a reflected light micrograph of a polished, carbon coated synthetic fluorite crystal. The identifying etched label, which is a feature of our standards, is invaluable for navigating in an electron beam instrument.
Of course, fluorine, being a very light element, emits only low energy X-rays which are easily absorbed, hence the need for a standard with plenty of F. Quantitative analysis of fluorine is particularly
difficult, as documented by Ottolini et al. (2000) Amer. Min. 85, 89-107. Fluorite has four good octahedral cleavages which results in polished surfaces often having a pitted
appearance where the cleavages come together in a re-entrant. This mineral gives its name to the element fluorine, and itself is named from the Latin fluere - to flow - in allusion to easy melting when used as a flux in the smelting of metals.
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