CompuServe Messages

>> If the granitic gravel shows no polishing, how about any quartz grains at the surface of the granite (or whatever)? Maybe the surface is just younger – I am guessing that as they weather, granite pebbles will be continually losing faster-weathering mineral grains and thus losing their whole surface more often than quartz pebbles, constantly returning to an unpolished surface.>> I think you are absolutely right. <<"Silica gel effect" does not suggest anything like surface melting to me, seeming to refer to some dissolving and redeposition or hydration and dehydration effect. << The SGE is something that happens quickly and while hard materials are contacting the surface. It is aparently not exactly melting, as you suggest, but does act as though the surface is melted. Our student got into this because of an interesting observation some one made. An archaeologist had found a phytolith "embedded" in the silica surface of a stone tool. If this was embedded in the surface as a result of the silica gel effect during the tool's use (in this case as a tool for cutting cereal grains, a sickle), it would be a very interesting way to find out exactly what people were doing with the tool. (this is part of a very large research effort to determine the uses to which stone tools were put). An alternative explanation could exist for the phytolith. That is, it is not really a phytolith, but part of a diatom, and is a componant of the fossiliferous flint from which the stone tool was made! In any event, determining whether or not the "silica gel effect" was real thus became an important part of this overall research program. Cheers, GTL – Greg Laden, Written 18-Sep-1994 @ 20:42:06 Using: Windows NavCIS PRO 1.25