Onyx is part of the chalcedony family of colored quartz, which includes agate, cornelian and jasper. It is usually seen in black but it can come in other colors. Sardonyx is onyx that is red to brownish in color.
The striking black and crisp lines of onyx makes it especially popular for jewelry. Because the lines can form in many different ways, each piece of onyx has a unique appearance. Onyx is also popular for cameos - when an image is carved into onyx, the color of the next band shows through. Onyx is opaque (meaning no light shines through it), therefore, it is usually cut into a smooth, rounded, polished dome called a cabochon.
Onyx has a variety of myths associated with it. Some cultures believe that it was supposed to drive away evil and high tempers. Other cultures believed it was to cool the passions of love and promote independence between lovers - which can be good or bad, depending on one's point of view. Some people even believed it was a symbol of discord, a belief probably suggested by the sharply divided lines in the stone.
||Black and white or gray, or black and red to brownish red
||Opaque variety of quartz with alternating black areas interspersed with lighter-colored lines. Color from silicon dioxide. Mohs' hardness rating of 7.