From an unused root (probably identical with that of shabah through the idea of subdivision into flashes or streamers (compare shabiyb) meaning to flame; a gem (from its sparkle), probably the agate -- agate.
Exodus 28:19 HEB:הַשְּׁלִישִׁ֑י לֶ֥שֶׁם שְׁב֖וֹ וְאַחְלָֽמָה׃ NAS: a jacinth, an agate and an amethyst; KJV: a ligure, an agate, and an amethyst. INT: and the third A jacinth an agate and an amethyst
Exodus 39:12 HEB:הַשְּׁלִישִׁ֑י לֶ֥שֶׁם שְׁב֖וֹ וְאַחְלָֽמָה׃ NAS: a jacinth, an agate, and an amethyst; KJV: a ligure, an agate, and an amethyst. INT: and the third A jacinth an agate and an amethyst