Quartz is the second most common mineral in the crust of earth and is made from silicon dioxide or SIO2.
Quartz can form as large blocks of interlocking crystals or massive quartz. When the crystal faces are easy to make out and well formed we call that macro or euhedral quartz. This is the type of quartz most of us think about when someone says quartz or quartz crystal.
Quartz also forms in crypto and microcrystalline habits, creating agates, jaspers, chalcedony, chert and a few other forms which the crystal shape and structure can only be seen under extreme magnification.