It about somebody who has these crystals that can steal and transfer pain, and I believe they are purple. For example, if somebody had a broken finger the crystal could take it from the person who had the broken bone, and give it to somebody else. They made armor out of it and weapons like a rapier or whatever.
This seems similar to The Healing Wars. The series has a blue metal called pynvium, which can be employed to store pain. However, it is also shaped into weapons that deal pain when used, or armor that under certain circumstances can be used to heal during combat. The mechanism is similar to what you describe (when pain is stored, the injury disappear, and the pain can be transferred to other people), and metal is very often crystalline, though there are metallic glasses. The main element that does not fit is the color: pynvium is blue, as I recall. If this is not the book you're looking for, it has remarkable similarities, though.
In that series, transferring pain was not a standard talent, though, nor a property of the crystals. Standard healers can only transfer pain from people to pynvium, but the pynvium itself has no such power. The protagonist, though...let's just say that the medical establishment has pretty much no idea of what is possible with pynvium and pain magic.