Diamond grit — also referred to as diamond powder — is a loose abrasive composed of finely crushed diamond particles, used in lapidary work to cut, grind, and polish gemstones and other hard materials. Because diamond is the hardest known natural substance (10 on the Mohs scale), grit derived from it is uniquely capable of working materials that defeat conventional abrasives such as silicon carbide, including corundum (ruby and sapphire, Mohs 9), chrysoberyl (Mohs 8.5), and diamond itself. Its role in the modern lapidary workshop is foundational: virtually every faceted corundum or diamond in commercial jewellery has passed through at least one stage of diamond-grit processing.

Production and Sources

Commercial diamond grit is produced by two principal routes. The first is the crushing and milling of natural diamond fragments — cleavage pieces, boart (low-grade, heavily included material unsuitable for gem use), and industrial off-cuts — into angular particles of controlled size. The second, and now dominant, route is the manufacture of synthetic diamond by high-pressure, high-temperature (HPHT) synthesis, followed by controlled fracture into grit. Synthetic diamond grit has been produced at industrial scale since the 1950s, and its consistent purity and particle morphology have made it the standard for precision lapidary and industrial grinding applications alike. The largest producers are located in Ireland (Element Six, a De Beers subsidiary), the United States, China, and Russia.

Grading by Mesh Size

Diamond grit is classified by mesh size, a figure derived from the number of openings per linear inch in the sieve through which particles pass. A higher mesh number indicates a finer particle. In lapidary practice, the grades fall broadly into three working ranges:

• Coarse (60–220 mesh): Used for initial shaping, sawing, and rough grinding. Particles in this range are large enough to remove material rapidly but leave a visibly scratched surface.
• Medium (325–600 mesh): Pre-polish and intermediate smoothing stages. Scratches from coarser grits are progressively refined.
• Fine to ultra-fine (1,200–100,000 mesh / 14 µm down to 0.1 µm): Polishing stages. At the finest grades, particle size is measured in microns rather than mesh, and the resulting surface approaches a mirror finish on hard materials.

Grit suppliers frequently express particle size in both mesh and micron equivalents on the same label; the two systems are inversely related and can be cross-referenced via standard conversion tables published by organisations such as FEPA (Federation of European Producers of Abrasives).

Application in the Lapidary Workshop

Diamond grit is applied to a lap — a rotating disc of metal (cast iron, copper, or tin alloy), resin-bonded composite, or ceramic — by mixing the grit with a carrier fluid, typically water, light oil, or a proprietary cutting fluid, and spreading it onto the lap surface. On metal laps, the particles are worked or charged into the surface by pressing a hard material against the spinning disc; the particles embed partially and present sharp edges to the workpiece. Resin and ceramic laps are more commonly used with a slurry that is continuously replenished rather than charged.

The choice of lap material interacts with grit grade: cast-iron laps are preferred for charging with coarser grits when cutting corundum or hard oxides, while tin or lead-alloy laps accept finer grits for pre-polish, and resin or ceramic laps are standard for final polishing stages. Contamination between grit grades — even a few coarse particles on a fine-polish lap — can introduce deep scratches that require returning to an earlier stage, so strict workshop discipline in segregating grits is essential.

Relevance to Specific Gemstone Species

For corundum (ruby and sapphire), silicon carbide abrasives are technically capable of cutting but are inefficient and wear rapidly; diamond grit at all stages is the professional standard. For diamond itself, cutting and bruting rely on diamond grit or diamond-impregnated tools, exploiting the fact that diamond's hardness varies with crystallographic direction — a phenomenon known as anisotropy — so that one diamond can abrade another along its softer directions. Chrysoberyl, spinel, topaz, and high-hardness garnets such as demantoid and tsavorite also benefit from diamond-grit processing at polishing stages, where conventional aluminium oxide or cerium oxide polishes may leave sub-optimal surfaces.

Industrial and Gemological Context

Beyond the gem lapidary, diamond grit is integral to the semiconductor, optics, and precision-engineering industries, where it is used to lap silicon wafers, grind optical flats, and finish hardened steel components. This broad industrial demand underpins a large-scale synthetic diamond manufacturing infrastructure that keeps lapidary-grade grit widely available and relatively affordable. For the gemologist, an awareness of diamond grit is practically relevant when assessing surface condition: a stone that has been re-polished with insufficiently fine grit will show residual parallel scratches under oblique illumination, a detail that can inform judgements about the quality of a recutting or repair job.