Schorl is a variety of Tourmaline. Commonly referred to as Black Tourmaline the mineral is rich in Iron. More specifically Schorl is a sodium iron aluminum boro-silicate. Its crystal structure is usually hexagonal as is most versions of Tourmaline. It has a hardness of 7 to 7.5 on the mohs hardness scale.
The chemical composition of Schorl is: NaFe2+3Al6(BO3)3Si6O18(OH)4