The twelve stones differed not only in color, but also in certain qualities peculiar to each, and both quality and color had especial reference to the tribe whose name it bore. Reuben's stone was the ruby, that has the property, when grated by a woman and tasted by her, of promoting pregnancy, for it was Reuben who found the mandrakes which induce pregnancy.
Simeon's stone was the smaragd, that has the property of breaking as soon as an unchaste woman looks at it, a fitting stone for the tribe whose sire, Simeon, was kindles to wrath by the unchaste action of Shechem. It was at the same time a warning to the tribe of Simeon, that committed whoredom at Shittim with the daughters of Moab, to be mindful of chastity, and like its stone, to suffer no prostitution.
Levi's stone was the carbuncle, that beams like lightning, as, likewise, the faces of that tribe beamed with piety and erudition. This stone has the virtue of making him who wears it wise; but true wisdom is the fear of God, and it was this tribe alone that did not join in the worship of the Golden Calf.
Judah's stone was the green emerald, that has the power of making its owner victorious in battle, a fitting stone for this tribe from which springs the Jewish dynasty of kings, that routed its enemies. The color green alludes to the shame that turned Judah's countenance green when he publicly confessed his crime with Tamar.
Issachar's stone was the sapphire, for this tribe devoted themselves completely to the study of the Torah, and it is this very stone, the sapphire, out of which the two tables of the law were hewn. This stone increases strength of vision and heals many diseases, as the Torah, likewise, to which this tribe was so devoted, enlightens the eye and makes the body well.
The white pearl is the stone of Zebulun, for with his merchant ships he sailed the sea and drew his sustenance from the ocean from which the pearl, too, is drawn. The pearl has also the quality of bringing its owner sleep, and it is all the more to the credit of this tribe that they nevertheless spent their nights on commercial ventures to maintain their brother-tribe Issachar, that lived only for the study of the Torah. The pearl is, furthermore, round, like the fortune of the rich, that turns like a wheel, and in this way the wealthy tribe of Zebulun were kept in mind of the fickleness of fortune.
Dan's stone was a species of topaz, in which was visible the inverted face of a man, for the Danites were sinful, turning good to evil, hence the inverted face in their stone.
The turquoise was Naphtali's stone, for it gives its owner speed in riding, and Naphtali was "a hind let loose."
Gad's stone was the crystal, that endows its owner with courage in battle, and hence served this warlike tribe that battled for the Lord as an admonition to fear none and build on God.
The chrysolite was Asher's stone, and as this stone aids digestion and makes its owner sturdy and fat, so were the agricultural products of Asher's tribe of such excellent quality that they made fat those who ate of them.
Joseph's stone was the onyx, that has the virtue of endowing him who wears it with grace, and truly, by his grace, did Joseph find favor in the eyes of all.
Jasper was Benjamin's stone, and as this stone turns color, being now red, now green, now even black, so did Benjamin's feelings vary to his brothers. Sometimes he was angry with them for having sold into slavery Joseph, the only other brother by his mother Rachel, and in this mood he came near betraying their deed to his father; but, that he might not disgrace his brothers, he did not divulge their secret. To this discretion on his part alludes the Hebrew name of his stone, Yashpeh, which signifies, "There is a mouth," for Benjamin, though he had a mouth, did not utter the words that would have covered his brothers with disgrace. 
The twelve stones in the breastplate, with their bright colors, were of great importance in the oracular sentences of the high priest, who by means of these stones made the Urim and Tummim exercise their functions. For whenever the king or the head of the Sanhedrin wished to get directions from the Urim and Tummim he betook himself to the high priest. The latter, robed in his breastplate and ephod, bade him look into his face and submit his inquiry. The high priest, looking down on his breastplate, then looked to see which of the letters engraved on the stones shone out most brightly, and then constructed the answer out of these letters. Thus, for example, when David inquired of the Urim and Tummim if Saul would pursue him, the high priest Abiathar beheld gleaming forth the letter Yod in Judah's name, Resh in Reuben's name, and Dalet in Dan's name, hence the answer read as follows: Yered, "He will pursue."
The information of this oracle was always trustworthy, for the meaning of the name Urim and Tummim is in the fact that "these answers spread light and truth," but not every high priest succeeded in obtaining them. Only a high priest who was permeated with the Holy Spirit, and over whom rested the Shekinah, might obtain an answer, for in other cases the stones withheld their power. But if the high priest was worthy, he received an answer to every inquiry, for on these stones were engraved all the letters of the alphabet, so that all conceivable words could be constructed from them.