The Petrographic Use of the Spindle Stage and Focal-Plane Screening in the Determination of the Optical Variation of Some Zoned Minerals

Hedley G. Wright
9 Moray Place, Edinburgh 3

Summary: The Equivibration Curve technique of Joel (1963) is used to determine the orientation of a zoned mineral on the spindle stage axis and an average value for 2V. A bracketing method enables the extreme values of each refractive index to be determined for sodium light on a single grain, using the Focal-plane Screening technique of Cherkosov (1960).

Mineralogical Magazine; December 1965 v. 35; no. 272; p. 656-660; DOI: 10.1180/minmag.1965.035.272.10
© 1965, The Mineralogical Society
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