The 12 Breastplate Stones: 7 Surprising Facts About the Precious Stones on the High Priest's Garment

1. The choshen (breastplate) was one of the eight garments worn by the kohen gadol (high priest) when he performed the service in the Temple. (The other seven garments were the ephod, the robe, the tunic, the turban, the breeches, the belt, and the tzitz.) The choshen's stones corresponded to the 12 tribes of Israel. Each precious stone symbolized a different tribe, whose name was inscribed on the stone.

2. The choshen was square-shaped, and each side measured a biblical 'zeret' (about 25 cm). It contained gold settings in which the 12 precious gemstones were embedded.

The choshen was made of fabric that was embroidered with precious threads of gold, blue, purple, scarlet, and fine linen. The choshen was placed on the kohen gadol's ephod and fastened to the ephod's rings with cords.

3. These are the Hebrew names of the gemstones:

Odem (attributed to the tribe of Reuben), pitdah (Simeon), bareket (Levi), nofech (Judah), sapir (Issachar), yahalom (Zebulun), leshem (Dan), shevo (Naphtali), achlamah (Gad), tarshish (Asher), shoham (Joseph – Manasseh and Ephraim), yashpeh (Benjamin).

Rabbenu Bachya writes: "Know that it is written in the books of natural wisdom that there are only twelve precious stones that are elemental and fundamental, and they are the roots of all other stones" (Rabbeinu Bachya, in his commentary on Parashat Tetzaveh, Chapter 28).

4. The commandment to make the choshen appears in Parashat Tetzaveh, where the Torah describes the process of fashioning the choshen, as well as the order in which the stones were embedded from top to bottom and right to left.

Beyond this, the choshen served an additional function, and the leaders consulted the Urim and Tumim before they went off to war. For this reason, it was also called "the choshen of judgment." The Torah tells us: "He shall stand before Eleazar the priest, who shall inquire for him by the judgment of the Urim before Hashem; at his word they shall go out, and at his word they shall come in, both he and all the children of Israel with him, the whole congregation" (Bamidbar 27:21).

According to the Sages, the message was conveyed through the gemstones that were engraved with the names of the tribes of Israel.  The stones would provide an answer to the question by illuminating different letters.

According to Rashi, the Urim and Tumim was the Divine name placed within the folds of the choshen that caused the letters to light up. According to the Rambam, the choshen stones themselves were the Urim and Tumim..

6. Aside from the names of the tribes, the names of Avraham, Yitzchak, and Yaakov and the words tribes of Yeshurun were also engraved on the stones (Babylonian Talmud, Tractate Yoma, end of Chapter Seven), so that all the letters of the Hebrew alphabet appeared, which enabled it to serve as the Urim and Tumim. 

According to the commentators (Rabbeinu Bachya, Chizkuni, Baal HaTurim), each gemstone contained six letters.

7. Today, we cannot identify the specific gemstones that were embedded on the choshen (aside from the yahalom, which is a diamond). Since the names of the gemstones are ancient, their exact meaning has been lost since the destruction of the Temple and the long exile.