Ron Geitgey       P H O T O G R A P H E R    —    S T O N E   S C U L P T O R Home     Background     Sculpture Gallery     Photo Gallery     Private Photo Sessions     Stone Queries     Merchandise     Contact S T O N E  Q U E R I E S         Contents       1       2       3       4       5       6       7       8       9       10       11       12   Stone Query 6 –  ROTTEN GRANITE   Ron Geitgey www.rongeitgey.com   Someone told me they were carving rotten granite. What is that?   The term granite brings to mind concepts of hardness, permanence, and intractability but granite outcrops and boulders can be weathered to a crumbly material, often brown stained, that may be easily carved even without carbide or diamond tools. "Rotten granite" is an informal term used rather accurately to describe this partially decomposed granite.   All rocks at or near the earth's surface are subject to weathering, changes brought about by physical, chemical, and biological processes. The end product is sediment and soil, although from a geological perspective it's not the end but simply a step in a great cycle toward a sedimentary rock and beyond. Rotten granite is part way there.   By geologic definition granite and granitic rocks contain visible grains of quartz, feldspar, and various iron-bearing minerals. All of these grains formed from molten material, cooling and crystallizing into a tight, interlocking three-dimensional puzzle. Subjected to rainwater, groundwater, organic acids, and biological activity the quartz changes very little, but the feldspar begins to alter to clay minerals and the iron-bearing minerals convert to brown, yellow, and red iron oxides, what artists know as ochre. Little of this would be noticeable in a human lifespan but the puzzle pieces begin to loosen.   Weathering moves inward from the rock surface or outward from cracks and fractures, any feature that allows water to contact the rock. With an appropriate set of fractures granite weathers much as an ice cube melts, from a cubic form to a rounded form, a boulder. A partially weathered boulder may still be coherent enough to carve. It won't take a polish and it may not even tolerate grinding and sanding but broad forms with rustic finishes could be carved. However, rotten granite may not be uniformly rotten, a core or other areas of unaltered material may remain. But this offers an opportunity to contrast stained, altered, and unaltered surfaces with only a minimal investment of carving time. Of course there is also the risk of the stone's simply falling apart with the first (or last) hammer blow.   As weathering progresses beyond any coherence, granite masses may disintegrate to sandy, granular debris called "grus" (from German for grit or gravel). This decomposed granite is used commercially for landscaping, road surfacing, and chicken grit.   Sculpture Northwest, November/December 2002 published by Northwest Stone Sculptors Association (NWSSA)   BACK TO TOP   Photos by Ron Geitgey  |  Website design by Anne Rutherford  |  © Ron Geitgey, 2009  All Rights Reserved.