The stones of it are the place - Among the stones of the earth sapphires are found. "The situation of the sapphire is in alluvial soil, in the vicinity of rocks, belonging to the secondary floetz trap formation, and imbedded in gneiss." Jameson. "The sapphire occurs in considerable abundance in the granitic alluvion of Matura and Saffragam, in Ceylon." Davy.
Sapphires - Compare the note at Isaiah 54:11. The sapphire is a precious stone, usually of a blue color, though it is sometimes yellow, red, violet. green, or white. In hardness it is inferior to the diamond only:
"In unroll'd tufts, flowers purpled, blue and white,
Like sapphire, pearl, in rich embroidery."
Shakespeare
"He tinctures rubies with their rosy hue,
And on the sapphire spreads a heavenly blue."
Blackmore
The mineral is, next to the diamond, the most valuable of the precious stones. The most highly prized varieties are the crimson and carmine red; these are the "Oriental ruby" of the traveler, and next to the diamond are the most valuable jewels hitherto discovered. The blue varieties - the sapphire of the jeweler - are next in value to the red. The yellow varieties - the "Oriental Topaz" of the jeweler - are of less value than the blue or true sapphire. Edinburgh Encyclopedia, article "Mineralogy."
And it hath dust of gold - Margin, or "gold ore." Literally, "The dusts of gold are in it." Gold is often found in the form of dust. It is obtained by washing it from the sand, and passing it over a fleece of wool, to which the gold adheres.

The stones - the place of sapphires - In the language of mineralogists, the gangue, matrix, or bed in which the sapphire is found. For a description of this stone, see on Job 28:16 (note).
Dust of gold - Or rather, gold dust.

The stones of it [are] the place (f) of sapphires: and it hath dust of gold.
(f) He alludes to the mines and secrets of nature, which are under the earth, into which neither souls nor beasts can enter.

The stones of it are the place of sapphires,.... In some parts of the earth its stones are a quarry of sapphires, put here for all precious stones: this is a most excellent precious stone, of a sky colour, with golden specks, and was one of the stones in the breast plate of the high priest; and by which are represented the pavement under the feet of the God of Israel, the throne of Christ, his bowels and affections for his people, the comeliness of them, and the glory of his church in the latter day, Exodus 24:10;
and it hath dust of gold; some parts of the earth abound with the dust of gold; its dust is gold, or it hath gold as plenty as dust; though some think this refers to the sapphire in the preceding clause, which, as Pliny says (d), has "pulvis aureus", dust of gold, in it, and shines and sparkles with golden points, or specks; and so say other writers (e); but the word used rather signifies clods, lumps, masses of gold, which better agree with the earth; and, besides, no very good reason can be given why there should be such a particular description of the sapphire; whereas the earth is the original of that, and of all the other things before spoken of.
(d) Nat. Hist. l. 37. c. 9. (e) Ruaeus de Gemmis, l. 2. c. 2.

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.

Sapphires - Of precious stones; the sapphire, is one of the most eminent, being put for all the rest. In some parts of the earth, the sapphires are mixed with stones, and cut out of them and polished. Hath - The earth continueth. Dust - Distinct from that gold which is found in the mass, both sorts of gold being found in the earth.