Jamieson, Fausset and Brown on Job 28:6

6. Sapphires are found in alluvial soil near rocks and embedded in gneiss. The ancients distinguished two kinds: 1. The real, of transparent blue: 2. That improperly so called, opaque, with gold spots; that is, lapis lazuli. To the latter, looking like gold dust, Umbreit refers "dust of gold." English Version better, "The stones of the earth are, &c., and the clods of it (Vulgate) are gold"; the parallel clauses are thus neater.