#0306 אַחְלָמָה 'achlamah {akh-law'-maw}

 perhaps from H2492 (and thus dream-stone); TWOT - 67b; n f

—Hebrew Word Study (Transliteration-Pronunciation Etymology & Grammar)

 1) amethyst, a gem in the third row on the ephod, breastplate
    of judgment worn by the high priest. Transliteration of the
    Septuagint word. Identification is not certain but is a
    purple stone perhaps a corundum or red or brown jasper.

—Brown-Driver-Briggs (Old Testament Hebrew-English Lexicon)

—Strong's (Hebrew & Chaldee Dictionary of the Old Testament)

—NAS Exhaustive Concordance of the Bible with Hebrew-Aramaic and Greek Dictionaries

 AV - amethyst 2; 2

—Exhaustive Concordance (KJV Translation Frequency & Location)