Two onyx stones - See Clarke on Exodus 25:7 (note).

And thou shall take two onyx stones,.... called from the colour of a man's nail, which they to resemble: the Targums of Onkelos and Jonathan call them stones of beryl, and so the Syriac version; the Septuagint, stones of emerald, and the Arabic version, crystal stones: but, according to Josephus (x), they were sardonyx stones, and in which Brannius (y) thinks he was right:

and grave on them the names of the children of Israel; the names of the twelve sons of Jacob, six on one stone and six on the other, as often mentioned, for which onyx stones are very fit; and they must be very large to have so many letters graved upon them; for there is no reason to believe the initial letters of their names only were engraved, but their whole names at length. In the Museum at Dresden is an oriental onyx which cost 48,000 dollars; it is of an oval figure, and its longest diameter is almost six inches, and in such an one might easily be engraved so many names: and Wagenseil makes mention of one in the possession of the bishop of Bamberg, in which were represented Christ sitting, and teaching his twelve apostles standing round him, of which he has given the figure (z): the onyx stone being of the colour observed, was a fit emblem of Christ in his human nature, and if the sardonyx, of him in both his natures; and as the twelve tribes of Israel were a figure of the church, their names being on two stones may denote both the Jewish and Gentile churches; these being precious stones on which they were engraven, may signify how valuable the church and its members are to Christ; and being alike there, their being equally loved of God, chosen in Christ, redeemed by his blood, interested in all the blessings of his grace, and shall enjoy the same glory; and their names being there, the distinct knowledge had of them by name, and being in ouches of gold, their dignity and safety, as afterwards declared.

(x) Ut supra. (Antiqu. l. 3. c. 7. sect. 5.) (y) De Vestitu Sacerd. Heb. l. 2. c. 18. sect. 4. p. 730. (z) Not. in Misn. Sotah, c. 9. p. 996.

Upon the shoulder-piece of the ephod two beryls (previous stones) were to be placed, one upon each shoulder; and upon these the names of the sons of Israel were to be engraved, six names upon each "according to their generations," i.e., according to their respective ages, or, as Josephus has correctly explained it, so that the names of the six elder sons were engraved upon the previous stone on the right shoulder, and those of the six younger sons upon that on the left.

And thou shalt take two onyx stones, and grave on them the names of the children of Israel:

28:6-14 This richly-wrought ephod was the outmost garment of the high priest; plain linen ephods were worn by the inferior priests. It was a short coat without sleeves, fastened close to the body with a girdle. The shoulder-pieces were buttoned together with precious stones set in gold, one on each shoulder, on which were engraven the names of the children of Israel. Thus Christ, our High Priest, presents his people before the Lord for a memorial. As Christ's coat had no seam, but was woven from the top throughout, so it was with the ephod. The golden bells on this ephod, by their preciousness and pleasant sound, well represent the good profession that the saints make, and the pomegranates the fruit they bring forth.