Onyx stone is a sedimentary rock, formed as stalactites and stalagmites in limestone cave interiors. It is formed of bands of chalcedony in alternating colors. Onyx is cryptocrystalline, consisting of fine intergrowths of the silica minerals quartz and moganite. Onyx’s fascinating patterns and unique translucent qualities are a result of its softer and somewhat more fragile qualities, and so careful thought must be given to the location of the onyx countertops and what their purpose is going to be. Onyx stone is well-suited for furniture pieces, bathrooms, and fireplace surrounds.