Agate vs. Onyx — What's the Difference?

Agate is a variety of chalcedony that comes in a wide range of colors and patterns, often used in jewelry and ornamental objects for its aesthetic appeal. On the other hand, onyx is a type of chalcedony characterized by its distinctive parallel banding, typically showcasing black and white layers, and is frequently used in jewelry and decorative items for its striking appearance.

The formation process of agate involves the filling of cavities in volcanic rocks or ancient lavas, where layers of silica cool and crystallize, resulting in its unique banded patterns. Whereas, onyx forms from the deposition of silica in cold water solutions, often in caves, leading to its straight, parallel bands.

Agate is prized for its translucency and variety of colors, including reds, greens, yellows, and blues, making each piece unique. On the other hand, onyx is most commonly associated with its black and white bands, though it can also appear in variations of red and brown, known as sardonyx.

The uses of agate extend beyond jewelry; it is also popular in making decorative items such as bookends, coasters, and tabletops due to its beautiful patterning and color variations. Onyx, however, is often selected for more refined and elegant jewelry pieces, as well as for architectural elements and intricate carvings, thanks to its striking color contrast and polishability.

Despite their differences, both agate and onyx share a hardness of 6.5 to 7 on the Mohs scale, making them durable choices for jewelry and decorative items. However, their appeal comes from their distinct visual characteristics: agate for its colorful, banded patterns, and onyx for its elegant, contrasting bands.