Abstract

Analysis of the Yule marble of Colorado by the small-circle net X-ray technique has revealed the existence and position of minor fabric features that cannot be completely discerned by a 100- or 200-grain universal stage analysis. These include a c-axes minimum in or at low angles to the foliation plane; a number of minor maxima at high angles to the major point maximum which is split into two or more submaxima; and a sufficient concentration of axes connecting the major split point maximum to the minor maxima to reveal a weak girdle pattern.

X-ray analyses of the c-axis direction were made from two contiguous portions of the same Yule marble specimen, with the orientation of the X-ray cuts with respect to the T section being different for each analysis. The fabric diagrams showed strong point maximum and interconnecting girdles in both cases, but different relative positions of these features with respect to megascopic coordinates. These results, along with a study of the optical fabric data in the literature, lead to the conclusion that the orientation of only the grossest aspect of the fabric is consistent from sample to sample and that the minor fabric features vary considerably within the domain of the hand sample.

An optical analysis of 500 c axes from the T section of one X-ray sample gives good agreement with the major features of the c-axis X-ray diagrams, including the splitting of the major point maximum; but only a hint of the other minor features can be: observed. New X-ray fabric diagrams for the [110] = a, [101] = r, and [012] = e directions of Yule marble show little a-axis orientation, other than a broad girdle in the foliation plane, and considerable concentration of the r and e directions into maxima and into girdles concentric about the split c-axis maximum.

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