The 2 black onyx stones placed on the shoulders were engraved with the names of the children of Israel by birth order. The 12 stones mounted in the breastplate were also to be the names of the children of Israel but I do not read that the placement was to necessarily be in birth order. Does tradition place the stones in birth order from right to left across the rows? Also, since Levi was set apart for the Lord and Joseph’s tribe was divided into Ephraim & Manasseh, how are these accounted for in the breastplate? Thank you.
ב"ה Shalom First allow to me say that the "shoham" stones mentioned in Exodus 28:9 are translated by Josephus (Antiquities 3:7:5, Wars 5:5: 7 as being sardonyx and it is the same in the Greek Septuagint. Its color is a mixture of white and red or brown. In regard to the breastplate, in Exodus 28;21 it states "Each one's name.. ", which according to some commentators means as the order of birth and in Hebrew they were written right to left.In the case of the breastplate the names of the tribes included Levy and Joseph is written as one tribe while Manasseh and Ephraim were not inscribed. All the best