Onyx
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Onyx is a typically black-and-white banded variety of agate, a silicate mineral. The bands can also be monochromatic with alternating light and dark bands. Sardonyx is a variety with red to brown band
Onyx with concentric banding
Cabochons of red onyx, also called sardonyx
Black onyx with white streaks
The Gemma Augustea is a Roman cameo produced 9–12 AD and carved in a two-layered onyx gem (19 × 23 cm).
Birthstone
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A birthstone is a gemstone that represents a person's birth period, usually the month. Birthstones are often worn as jewelry or a pendant necklace.
Onyx
…Jasper – Chalcedony variety colored by iron oxide Birthstone – Gemstone representing a person's birth month Rudler, Frederick William (1911). "Onyx" . Encyclopædia Britannica. Vol. 20 (11th ed.). p. 118…
Recreation of the high priest's breastplate in front of the central Sephardic synagogue in Ramat Gan, Israel
Garnet, the birthstone for January
Amethyst, the birthstone for February
Aquamarine, the birthstone for March