Some Crystals can be toxic. If you are obtaining crystals make sure you're sure what they are. I personally have been sold two different toxic crystals..
Some healers use crystals for physical healing. I do believe this is possible. Unfortunately, I do not know much about physical healing so I will leave that up to those smarter than me.
Crystals grow in many ways. Some grow from mineral rich water similar to how they make rock candy (you can DIY it as welL!). Others grow from vapor or melted rock ooze. The type and composition of a crystal depend on the pressure, temprature, and minerals present. 
