Onyx is a variety of quartz in compact micro-crystalline masses, with an uniform opaque or semi- opaque color. Its tonalities touch the colors of red, dark brown and the entire range of greys until black, presenting a surface drawn by stripes ans crystalline shades. Onyxes are less compact than marbles and present flaws and natural cracks that normally are resin treated, so that a uniform and well closed surface results.
