Smokey quartz is a brown to black gem variety of quartz, belonging to the rock crystal family of stones. All rock crystals are composed of SiO2 They form according to a trigonal crystal structure, and have a hardness of 7 on the Mohs scale.
Tourmaline is the name given to a very chemically complex (A(D3)G6(Si6O18)(BO3)3X3Z) family of stones. With slight chemical differences it comes almost every colour varying from light to dark. All types of tourmaline form according to a hexagonal crystal system and have a hardness of 7.5 on the Mohs scales. These are considered precious stones and some varieties are highly valued.