It can be broken in any direction, not just along crystal faces. There are many homogeneous rocks and they vary considerably in their mechanical properties. For our purposes, we need a hard rock, that is, one that is not easily scratched. Quartz is very hard, transparent, hexagonal prizmatic crystals. When crushed, it is a white powder.
Any color is due to impurities.
Quartz crystals can be formed either by the slow cooling of molten silicate rocks, or by precipitation from water that is saturated with dissolved silica. While pure quartz is both hard and beautiful, its overt crystal structure makes this mineral less than ideal for making stone tools. They are formed by precipitation from water that is saturated with dissolved silica. They may be brightly colored due to the presence of impurities. Varieties of chalcedony include agate, flint, and petrified wood.