Onyx beads Color: black with white stripes. Sizes between 4 and 14 mm. Country of origin: Brazil. Onyx gemological information: Note: in gemology, a distinction is made between black agate and onyx. In gemology, black onyx is an agate with alternating bands of white and black. Lithotherapy extended the definition of onyx to a completely black stone. You should know that a large part of black agates are tinted to present this perfectly solid color. Density: between 2.58 and 2.65. Hardness: between 6 and 7. Crystal system: trigonal. Family: microcrystalline quartz. Break: irregular. Cleavage: none