Hoshen, the breastplate, first worn by the High Priest Aaron, and subsequently worn by every High Priest in the Temple while performing holy duties. There were 12 precious stones in the Hoshen, as mentioned in Book of Exodus: Ruby, Garnet, Citrine, Blue Topaz, Topaz, Sapphire, Peridot, Onyx, Emerald, Diamond, Amethyst, Aquamarine. Various Jewish sources teach us that in addition to representing the Twelve Tribes of Israel, each stone has served as an expression of faith and optimism throughout the generations.
The Breastpiece - Exodus 28
15 "Fashion a breastpiece for making
decisions-the work of a skilled craftsman. Make it like the ephod: of
gold, and of blue, purple and scarlet yarn, and of finely twisted linen. 16
It is to be square-a span 
long and a span wide-and folded double. 17 Then mount four rows
of precious stones on it. In the first row there shall be a ruby, a topaz
and a beryl; 18 in the second row a turquoise, a sapphire 
and an emerald; 19 in the third row a jacinth, an agate and an
amethyst; 20 in the fourth row a chrysolite, an onyx and a
jasper.  Mount them in
gold filigree settings. 21 There are to be twelve stones, one
for each of the names of the sons of Israel, each engraved like a seal
with the name of one of the twelve tribes.