On the breast plate of the high priest as in Exodus 28:1721 there was twelve precious stones.

These 12 precious stones represented the12 tribes of Israel, and each stone was engraved containing the inscription of the name of the tribe of Israel.

Jacob had twelve sons (who became the twelve tribes of Israel), and each son’s name was inscribed upon the stone engraved on the breastplate.

Exodus 28:15-21:

15 “You shall make the breastplate of judgment. Artistically woven according to the workmanship of the ephod you shall make it: of gold, blue, purple, and scarlet thread, and fine woven linen, you shall make it. 

16 It shall be doubled into a square: a span shall be its length, and a span shall be its width. 

17 And you shall put settings of stones in it, four rows of stones: 

The first row shall be a sardius, a topaz, and an emerald; this shall be the first row; 18 the second row shall be a turquoise, a sapphire, and a diamond; 

19 the third row, a jacinth, an agate, and an amethyst; 20 and the fourth row, a beryl, an onyx, and a jasper. They shall be set in gold settings.

21 and the stones shall have the names of the sons of Israel, twelve according their names…