Onyx and opal are both gemstones that have been used in jewelry for centuries. Onyx is a black or dark-colored stone, while opal is a milky white stone with flashes of color. Both stones are highly valued for their beauty and rarity. Onyx is often used to make rings, necklaces, and other pieces of jewelry, while opal is often used to make earrings, pendants, and brooches. Both stones are also popular for their metaphysical properties, such as protection, healing, and luck.