I had heard that quartz responds to heat treating, so I decided to test high grade quartz, quartzite and something that resembles metabasalt. The flakes, no more than an inch thick, were buried a few centimetres below the surface. A small fire was made on top and maintained for between 1 and 2 hours.
I then brushed the coals aside and let the ground cool for a little while. My immediate reaction when digging up the flakes were that the pieces of quartz seemed more shiny and glossy. There was no visible difference on the quartzite and metabasalt.
When testing the pieces I found that the quartz knapped much easier. The flakes travelled easier and didn't step in the regular fashion. It also felt sharper. On the quartzite, which supposedly doesn't respond to heat treating I found a small positive change, although it may be just my bias. The metabasalt just became more brittle and crumbled under any flaking.
I didn't expect any change during such a short time of exposure to such relatively small temperatures. As the results were quite pleasing, I'm not sure much more would be recommended with the quartz, since it may become too brittle, but it may be worth experimenting with higher temperatures and/or longer time in the ground with quartzite.
