Measured 2θ values of the 201, 060, and 204 diffraction peaks of natural and synthetic alkali feldspars empirically can be linearly related to the a, b, and c cell parameters, respec lively. The structural state of many alkali feldspars may be estimated directly from a plot of 2θ (060) against 2θ (204) prepared for feldspars of known structural state. Feldspars having anomalous cell dimensions may also be recognized on such a plot. Composition of feldspars having normal cell dimensions may be determined from 2θ (201). Starting parameters for a computer refinement of the cell may be obtained from equations relating cell dimension to 2θ value of a single diffraction peak for a wide variety of natural, synthetic, and cation-exchanged alkali-feldspar phases. The ‘three-peak’ method permits any geologist who has access to an X-ray diffractometer to describe and name alkali feldspar phases commonly encountered in petrologic studies.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not have access to this content, please speak to your institutional administrator if you feel you should have access.