MONOCLINIC ORTHOCLASE CRYSTALS HAVING AUGEN AND TRICLINIC SHAPES BY REARRANGEMENT OF GRANITIC MINERALS UNDER STRESS

Shapes of monoclinic orthoclase crystals deviate from monoclinic when grown under stress. Augens lack faces. Other triclinic shaped crystals have recognizable forms and are nearly euhedral, but are crooked to the eye, with angles between faces (001) and (010) of 91ø to 94ø (compared to 90.0ø for orthoclase and 90.5ø for microcline). Crooked orthoclase crystals were reported by Goldsmith and Laves from the Lincoln porphyry, near Leadville, Colorado. They occur in Papoose Flat-type (PF-type) plutons of western U.S., which were subjected to post-consolidation processes. Augens and crooked shapes at Papoose Flat formed by passive growth in stress fields. Orthoclase crystals in PF-type plutons tend to separate whole, and are simple combinations of monoclinic forms. External features can be observed. Magmatic host minerals include medium-sized sub-hedral grains of non-zoned orthoclase. Evidences of physical distortion are lacking, such as disrupted internal features or conversion to microcline. To measure deviations from monoclinicity in random cuts of polished surfaces and thin-sections requires difficult to obtain views along a-axes. Internal features of PF-type crystals include preferentially concentrated, oriented minerals (hour glass textures), and concentric layers, oscillatorily zoned with regard to Ba and K. Such textures result from kinetics of growth controlled by differential rates of diffusion of components in fluids on mineral surfaces in diverse settings, including igneous, metamorphic and diagenetic. At Papoose Flat, augens and crooked crystals (semi-augens?) formed later than border zones of foliated granite, veins, and dikes. Oriented internal features parallel external shapes, from centers to margins. During growth, each crystal "knew" its final shape, which is not consistent with growth from magma or deformation, but accords with steadily maintained stress at growth sites. Two generations of K-feldspar observed by the author in granites of Europe and Asia, and reported in Africa, suggest a widespread nature of fascile rearrangements after emplacement.