Exodus 35:9 Kabbalah

וְאַ֨בְנֵי־שֹׁ֔הַם וְאַבְנֵ֖י מִלֻּאִ֑ים לָאֵפ֖וֹד וְלַחֹֽשֶׁן׃

and onyx stones, and stones to be set, for the ephod, and for the breastplate.

Read kabbalistic (mystical) interpretation of Exodus 35:9: and classical mystical sources.