Leshem is the ninth stone in the list of twelve set into the High Priest's breastplate at Exodus 28, assigned there to the tribe of Dan, and it appears again in the parallel list at Exodus 39. Those two passages are the whole of its attested use in the Hebrew Bible. There is no second context, no descriptive aside, no narrative in which someone handles a leshem and says something about it, and no cognate use in a securely dated inscription that would let a philologist cross-check the word against a known object.
That absence is the entire problem, and it is worth stating plainly, because the situation is easy to mistake for one where the evidence is merely thin. It is not thin. For this word there is one list, repeated once.
The translation history that follows is a record of successive judgment calls rather than of accumulating knowledge. The Septuagint translators rendered the word with a Greek term whose own referent is not securely known. The Vulgate made its choice. The King James translators produced ligure, a word that survives in English very largely because of this verse, and later English versions offer jacinth, opal and others in its place. Each rendering inherits its predecessors' reasoning, and no new evidence enters the chain at any point, which is why the disagreement visible between modern Bibles is not a sign that one of them has found something the others missed.