Stoney mentioned Granite (speaking of his hard head) so I thought I would do a write up about this common yet not really talked about stone ;)
Granite is a wonderful and highly valued stone. It is mostly comprised of Quartz and feldspar. It is very common and can be found practically in every country. It comes in shades of grey, pink, yellow, white and green. It is good to help people that are having a hard time believing in something(ex. reality of magic). It is good for building long lasting relationships of all kinds. Think strength and solidity. It usually looks like a blend of several stones because it has many colors(in some varieties). It is good for building/healing muscle and bone tissues. It can help when you need strength of willpower and of the mind. It is also used for counter tops, floors and pillars because of its strength, durability and beauty :)
My source is my notes from college.