It must be my dyslexia but I am having trouble following pindac and nandric.
@pindac, styluses are typically made of diamond which is the hardest jewel.
@nandric, there are large models of all the styluses you can look at. It all has to do with the angles the stylus is ground at. It is a pretty incredible process which I am sure you can see online. The diamond itself is dirt cheap, pennies. It is the process of shaping it that results in the expense. The more complex shapes are probably made possible by robotic control of the process.