Thanks as always for the replies.

My survival interest in knapping is because: (1) there is so much garbage typically available, including porcelain and glass, and (2) enough knappable rock (flint, chert, obsidian, sandstone, agate, chalcedony, etc.) enough places that, (3) it seems as sensible to learn to identify and use it in the field, as it does to learn to identify and work with edible and useful plants and animals.

Field expedient tools and weapons could make the difference, yes?