They were for a memorial before the LORD
This is from the King James Bible Exodus 28:21,29 & 30
21And the stones shall be with the names of the children of Israel, twelve, according to their names, like the engravings of a signet; every one with his name shall they be according to the twelve tribes.
29And Aaron shall bear the names of the children of Israel in the breastplate of judgment upon his heart, when he goeth in unto the holy place, for a memorial before the LORD continually.
30And thou shalt put in the breastplate of judgment the Urim and the Thummim; and they shall be upon Aaron's heart, when he goeth in before the LORD: and Aaron shall bear the judgment of the children of Israel upon his heart before the LORD continually.
If you look up precious stones in the Bible, you'll find articles on their meanings.
A military breastplate was a 'cuirass'
a breastplate is used to protect the internal organs, stomach, and the torso it was also used in the middle ages
Aegis.
no you can not
The aegis
Aegis
On average, about 2 - 2.5mm thick. However, the very centreline of the breastplate might be thicker, perhaps 3.5mm thick at most, and the edges of the breastplate at the sides might be as little as 1.0mm thick.
Stone is a unit of measurement for weight. As such 15 stone would mean 210Lbs. 1 Stone = 14 Lbs
What does Stone mean by the hidden stories in numbers
Breastplate, helmet and shield.
Hephaestus