The Kohen Gadol donned the choshen, breastplate, and wore the names of the twelve tribes of Israel on his chest. The fact that each tribe was present on the heart of the High Priest showed his mission and that of the Beis Hamikdash, to unite the Jewish people. Let us delve into the details of the stones to glean further lessons.
Most commentators state that the 12 stones were square. Ibn Ezra states that they were round and one source states they were hemispherical. Rabbeinu Bechaya explains that each stone contained six letters which spelled out the names of the 12 tribes and the names of the three Patriarchs as well as the phrase, “shiftey yishurun, the tribes of God (the Straight One, see Yuma 73b). He explains that the 6 letters on each stone express the message that the tribes of Israel were the reason for the 6 days of creation and the continued existence of the world. Additionally, 12 stones with 6 letters each equals 72 which corresponds to God’s 72 letter name and the 72 hours that made up the day part of the 6 days of creation (12 hours of daytime multiplied by 6, equals 72). The Kohen Gadol wore this great vestment and used it to ask questions of God and to receive answers through Divine Inspiration.
Commentators discuss which stone corresponded to which specific tribe. Rabbeinu Bechaya explains each stone and why that particular tribe was represented by that specific stone. Let us discuss some of them. Reuven had the “odem, carnelian (ruby)” which is red like blood, just as in his life he had found the dudaim which helped with childbirth. This stone helps one have a safe pregnancy and delivery. It also represents judgment as Reuven was judged harshly and repented for his sin with Bilhah.
Pidtah was Shimon’s stone and Rabbeinu Bechaya interprets it to be the emerald (prase) which was bright green. Shimon’s tribe sinned when Zimri committed a terrible rebellious act against God and his nation causing his tribe members to turn green with embarrassment. It appears to me that attention is given to the sins of Reuven and Shimon specifically because the Beis Hamikdash was a place of scrutiny, personal introspection and forgiveness.
Barekes was the stone of Levi which was bright carbuncle, known to make those who ingested it smart. Levi’s tribe was made up of the Jewish scholars and leaders. Nofach was the stone of Yehuda and it was green emerald. This hinted to Yehuda’s face which turned green after the incident the sale of Yosef and the episode with Tamar. Yissaschar was sapir (sapphire) which was the color of ticheles, the same as the luchos. Zevulan, the great supporters of Torah were the yahalom (pearl according to R. Bechaya) which brings about rest and sleep. Dan was the leshem (topaz), Naftoli was the turquoise shibo (agate); Gad the achlama (crystal) which strengthens the heart. Asher was the tarshis (chrysolite) which was oil colored; Yosef was the shoham, onxy, a stone that gives favor (chane) to one who bears it. Binyomin was the yashpeh (jasper) which was black red and green.
The above listed follows the opinion of Rabbeinu Bechaya in order and definitions. There is much depth contained in this section of the Torah as every word of the Torah contains worlds of knowledge. A careful study of the topic reveals many fascinating lessons, ideas and concepts relevant to gemology.