Exodus 28:19 Kabbalah

וְהַטּ֖וּר הַשְּׁלִישִׁ֑י לֶ֥שֶׁם שְׁב֖וֹ וְאַחְלָֽמָה׃

and the third row a jacinth, an agate, and an amethyst;

Read kabbalistic (mystical) interpretation of Exodus 28:19: and classical mystical sources.