ABSTRACT

Examination of quartzose sandstones with the scanning electron microscope reveals details and complexities not discernible with a petrographic microscope. Incipient quartz overgrowths occur either as growths with poorly defined crystal facies that are loosely interconnected over the surface of the detrital nucleus or as isolated growths with well defined crystal faces. If sufficient void space is present these incipient overgrowths may enlarge to partly envelop the nucleus and form well defined crystal faces. This appears to take place in the following ways: (1) overlap and/or mergence of individual subunit overgrowths with the same crystallographic orientation unitl so tightly packed that an atom cannot distinguish between subunits and growth continues as a single crystal; (2) envelo ment of earlier multiple overgrowths by an outer shell so that the underlying complex nature of the overgrowth is masked.

The crystal lattices of the overgrowth and nucleus are connected at isolated points. Much of the area between overgrowth and nucleus is void space, which forms the "dust" line visible in thin section. Secondary quartz probably eventually infills many of these voids, which destroys the "dust" line unless impurities are present also.

Presolved surfaces between quartz grains vary from relatively smooth to rough with ridges, knobs, furrows, and pits. A pressure solution surface may have a series of ridges and furrows, commonly in a radial pattern, along the margin.