Feldspar

Feldspar is a very common rock.  It is made up of a group of aluminum silicate minerals—the most abundant on Earth—containing potassium, sodium, or calcium. These minerals are key parts of igneous, metamorphic, and sedimentary rocks, making up about 60% of the Earth's outer crust.

However because Feldspar is SO incredibly common as a stone I’ve noticed that it can be a little tricky to track them down as beads.  

Feldspar has a hardness of 6 to 6.5 on the Mohs Hardness Scale.