Êxodo 28:9

Two onyx stones. — The shôham of the Hebrews has been regarded by some as the emerald, by others as the beryl; but it is probably either the stone usually called the onyx, or that variety which is known as the sardonyx — a stone of three layers — black, white, and red. (See Joseph., Ant. Jud., iii. 7, § 5.) Emeralds could not have been cut by any process known at the time. Onyx and sardonyx were used from a very early period, as stones for signets, both in Egypt and elsewhere.

And grave on them the names of the children of Israel. — That gem-engraving was practised from a remote antiquity both in Egypt and in Babylonia appears from the remains found in those countries. The signet cylinders of Chaldæan kings are regarded by the best Assyriologists as going back, at least, to B.C. 2,000. The signets of Egyptian monarchs reach, at any rate, to the twelfth dynasty, which is perhaps nearly as early. The hardest kinds of stone — diamond, ruby, emerald, sapphire, topaz — defied the art of the time; but stones of the second class — sard, carnelian, onyx, beryl, jasper, lapis lazuli — readily yielded to the engraver’s tools. There is no difficulty in supposing that among the Israelites were to be found persons who had been engaged in Egyptian workshops during the servitude, and were acquainted with Egyptian art in all its principal departments. The “names” to be engraved were doubtless the “tribe” names, as explained by Josephus.