My Opinion: Obsidian is nature's glass and has been used around the world for many thousands of years. Glass like obsidian comes in many different knapping able forms. I have found some of it in the Oregon Buttes that is very hard and some that is quite soft. Looking at points made in Oregon and South America that remain in tact after many years on or in the ground you need not question their durability. So I would say glass works just fine and believe it or not some very crude ones will get the job done. I saw Hawk Huston kill a Big snake in Texas and a smaller snake there, and then a turkey in Wyoming with the same butt ugly point. I used to have a source of slag glass from Michigan that I used for points for many years and that is a form of glass! Killed a big ole cow elk out of Reedsport, Oregon with a slag glass point! A/Ho Joe