--> ABSTRACT: Internal Architecture of Quartz Revealed by Deep Etching in HF, by Robert L. Folk, Karl Hoops, and Susan Ide; #91030 (2010)

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Internal Architecture of Quartz Revealed by Deep Etching in HF

Robert L. Folk, Karl Hoops, Susan Ide

We have etched quartz by submerging it for up to an hour in boiling, concentrated HF and then studying it with the SEM. This procedure reveals great differences in solubility between several varieties of quartz, and also within single crystals. Euhedral, water-clear, vein quartz prisms from Lemont, Pennsylvania, etch to form deep slots parallel with the c axis and perpendicular to prism faces; slots from neighboring faces collide at 60° angles as etching propagates them toward the central axis of the prism. Clear Arkansas vein quartz crystals show micro-wide etch tubes up to 1 mm long converging inward from prism faces, sometimes meeting in etched-out negative crystals. Sedimentary quartz overgrowths etch out much more rapidly than do most parent sand grains, and form spongy masses having a lineation parallel with the c axis. Volcanic quartz grains are very resistant to etching, and stretched metamorphic quartz etches in ribbons paralleling the c axis. Etching brings out great he erogeneities in quartz solubility from one type to another, and also shows solubility differences on a micron scale within single crystals, perhaps due to growth defects in the crystal lattice or due to trace elements.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.