Rock Polishing Supplies: Grit, Oxide and Diamond Compound

Understanding Abrasive Types

In lapidary, the journey from rough stone to a finished, high-gloss gem requires working through a series of abrasives—each one progressively finer and more precise.

These abrasives fall into three main categories: grits, oxides, and diamond compounds. Each plays a critical role depending on the stone’s hardness, your polishing method (cabbing, faceting, tumbling), and the type of finish you want.

Grits: Shaping and Smoothing the Foundation

In lapidary work, grit refers to the abrasive particles used to grind, shape, and polish stones and gemstones.

These particles vary in size, and the size is typically measured by a grit number—where a lower grit number means coarser, larger abrasive grains, and a higher grit number means finer, smaller grains. Starting with a coarse grit, such as 60 or 80, is essential for removing rough edges or shaping the stone.

60 Grit has a large particle size that you can see

120 Grit has a smaller size and is harder to see

1000 Grit is a very fine material and you cannot see the individual small pieces

 As the grit size increases—moving through 220, 400, 600, and up to 1000 or more—the abrasiveness decreases, allowing for more refined smoothing and surface preparation.

The choice of grit size at each stage determines how quickly material is removed and how smooth the stone’s surface becomes, ultimately affecting the final polish and appearance.

The progression of grits in lapidary is critical because it controls the quality of the finished gemstone and the efficiency of the process. After the initial shaping with coarse grit, medium grits refine the stone by removing scratches and imperfections left by the previous stage.

Fine grits, typically 600 to 1000, are used to prepare the stone for polishing by smoothing the surface to a near-gloss finish. Some lapidaries then move to ultra-fine abrasives like diamond pastes or oxides for the final polishing step. 

This gradual refinement reduces the risk of deep scratches or surface defects, which would detract from the stone’s clarity and shine. Skipping grit steps or rushing the process can result in a less brilliant finish and require reworking to fix.

Grit is most commonly made of silicon carbide, but can also be made out of aluminum oxide, or industrial diamond, and they’re used during the early shaping and smoothing phases.

Silicon carbide is affordable and works well on medium to soft stones, while aluminum oxide is a slightly slower-wearing, versatile option.

Diamond grits are more expensive but necessary when working with very hard materials like sapphire, spinel, or quartz.

Oxide Polishes: Chemical Shines for Softer or Vitreous Stones

Once your stone is shaped and smooth, oxides come into play for polishing. These powdered polishing compounds rely on both mechanical and chemical interaction with the stone’s surface, and they’re often used with felt, leather, or canvas polishing pads.

Three of the most commonly used oxides in lapidary are cerium oxide, tin oxide, and aluminum oxide—each with its ideal use cases.

Cerium Oxide Powder

Cerium oxide is best for glassy or vitreous stones like quartz, obsidian, and fluorite. It creates a soft chemical reaction on the surface, gently breaking down microscopic ridges while also producing a brilliant polish. It’s usually mixed with water to form a slurry and applied to a felt or leather wheel.

It works particularly well on a flat lap or a polishing disk, where the entire surface can be evenly treated. Many lapidarists prefer cerium oxide for faceted quartz or tumble-polished agates, as it gives a high-luster finish that’s difficult to match.

Tin oxide, on the other hand, is an excellent all-purpose polish, especially for softer, porous, or moisture-sensitive stones like opal, turquoise, and calcite. Tin oxide doesn’t have the same chemical aggressiveness as cerium but creates a smooth, clean shine when used with a soft polishing pad. It's also a safer choice for stones that may stain easily, as it has a lower risk of discoloration.

Tin Oxide

Aluminum oxide, particularly the ultrapure variety known as Linde A, is a favorite for certain stubborn stones that don’t respond well to other compounds. It’s especially useful on stones that tend to undercut (where softer spots wear faster than hard ones), such as petrified wood, chrysocolla, or rhodonite.

It can be used in powder form with water, or applied to a polishing pad in paste form.

When using oxides, cleanliness is key. Always use dedicated buffing pads for each compound, and wash your stones between stages to prevent contamination—especially from coarse grit residues.

Oxides are ideal when you’re looking for a balance between economy and polish quality, particularly if diamond paste is outside your budget or unnecessary for your stone type.

Diamond Paste and Powder: The Finishing Touch for Hard Stones

For very hard materials or when you want a mirror-finish, diamond paste or powder is the go-to abrasive. Diamond paste is made from finely ground industrial diamonds suspended in a water- or oil-based carrier.

The micron rating of the paste tells you how fine it is, with 1 micron equal to approximately 14,000 mesh/grit size. 

• 14µm (~1200 grit) for pre-polishing
• 6–3µm (~3000–8000 grit) for refining
• 1µm to 0.25µm (~14,000 to 100,000 grit) for final high-gloss polishing.

Diamond paste is incredibly versatile and works on almost any stone but shines when used on high-hardness materials like corundum, spinel, garnet, agate, and even jade. It’s typically applied to metal laps (like BATT or copper) or softer materials like leather or canvas pads.

Many lapidaries dab tiny dots of the paste across the pad and then rub it in with a finger, tool, or extender fluid to evenly distribute the abrasive. For best results, keep the surface slightly damp—not soaking—and apply light to moderate pressure.

One of the key advantages of diamond paste is control and precision. You can stop at any stage and assess the surface before deciding whether to continue or step back a grit. The paste is also long-lasting; a little goes a long way, and with proper care, it can be reused several times.

Alternatively, diamond powder can be sprinkled directly onto a lap and combined with an extender or water spray. This is more common in flat lap setups or in commercial polishing environments where large volumes of stones are processed at once.

Diamond Powder

Because diamond is neutral in color and doesn’t stain, it’s also a preferred option for white or translucent stones, where oxide residues might leave discoloration. However, it can be overkill for softer materials, where a gentle oxide polish is often more effective and less expensive.

Diamond Paste

Grit, oxide, and diamond compound are essential abrasive materials used in lapidary to shape, smooth, and polish stones, each serving a distinct purpose in the process.

Grit generally refers to coarse to fine abrasive particles—like silicon carbide or aluminum oxide—that grind away rough surfaces and gradually refine the stone’s shape and texture.

Oxides, such as cerium oxide or tin oxide, are much finer abrasives typically used in the final polishing stages to bring out a high-gloss shine and smooth finish on softer stones.

Diamond compounds consist of ultra-hard diamond particles suspended in a paste or powder, offering the most aggressive and precise polishing for hard materials like quartz, corundum, and other tough gems.

While these three compounds are among the most commonly used in lapidary, there are many other abrasives and compounds tailored to different stones and polishing needs.

Each has its unique grit size, hardness, and ideal use case depending on the stage of polishing and type of material being worked on.

To better understand the full range of available compounds, their grit sizes, and when to use each one, check out this in-depth chart that breaks down many more abrasives and their ideal applications for lapidary work. This guide can help you choose the right compound for every step, ensuring the best results for your stones.

When working with different lapidary techniques like cabbing, faceting, or tumbling, the selection and use of grits, oxides, and compounds vary significantly to suit the unique demands of each process.

In cabbing, which involves shaping and polishing rounded or domed stones, the progression typically starts with coarser grits to shape the rough material, followed by finer grits to smooth the surface.

Afterward, polishing compounds such as diamond paste or cerium oxide are applied to achieve a glossy, mirror-like finish that highlights the stone’s color and clarity. Because cabochons often feature curved surfaces, careful control of grit progression and polishing is crucial to avoid unevenness or scratches.

Faceting requires an even more precise approach since the goal is to create flat, angled surfaces that reflect light brilliantly. Here, lapidaries often rely on very fine diamond compounds for the polishing stages, paired with carefully chosen oxide compounds for softer stones, to create sharp, clean facets without scratches or pits.

Tumbling, on the other hand, is a more automated process that uses a sequence of grits and polishing compounds inside a rotating barrel to smooth and polish irregularly shaped stones in bulk. Tumbling typically starts with coarse grit to remove rough edges, gradually moving to finer grits and finishing with oxides or diamond compounds to bring out a polished shine.

Understanding how each abrasive fits into these different lapidary methods helps ensure the best finish and quality for each type of project.

Here is a more detailed breakdown for each type of workflow: Cabbing, Tumbling, and Faceting.

1. Cabbing Workflow – Shaping and Polishing Cabochons (Agate, Jasper, Turquoise, etc.)

The cabbing process—used to create smooth, domed cabochons—typically begins with coarse grinding to shape the rough stone. For hard materials like agate, jasper, or petrified wood, lapidaries often start with 80-grit diamond or silicon carbide wheels, which rapidly remove bulk material and establish the overall cabochon outline and dome profile. Softer stones like turquoise may instead begin with 100 or 180 grit to avoid chipping or overcutting.

Once the basic shape is established, the stone progresses through a series of finer grits: 220, 280, 600, and often 1200 or 1500 grit. At each stage, the goal is to remove the scratches left by the previous grit while refining the surface. Most cabbing machines use water-cooled diamond wheels or belts, which help minimize dust and keep the stone cool during grinding. Between each stage, it's critical to thoroughly rinse both the stone and your hands to avoid cross-contamination, which can reintroduce coarse scratches during polishing.

After the 600 or 1200 grit stage, the stone moves into the pre-polish phase. Many lapidaries use 3,000 or 8,000 grit diamond belts or pastes at this point. These fine abrasives begin to produce a soft sheen and prepare the surface for final polishing. For most quartz-family stones, a final polish with cerium oxide on a felt or leather pad yields a high-gloss, glass-like shine. Cerium is a fast-working oxide well-suited for vitreous and translucent materials.

For more porous or soft stones like opal, turquoise, or lapis lazuli, tin oxide or aluminum oxide (Linde A) may be a better choice for final polishing. These are gentler and less likely to undercut or stain the surface. Advanced cabbers working with very hard stones—like sapphire, garnet, or zircon—may finish with 14,000 to 50,000 grit diamond paste, applied with a leather pad or BATT lap for superior clarity and brilliance.

Some lapidaries go even further, using 100,000 grit diamond powder for museum-quality or competition-grade cabochons, though this step is optional for most hobbyists.

🔍 Pro tip: Always polish at lower RPMs (~400–800), use minimal pressure, and clean your polishing pads often to prevent dulling the final finish.

2. Faceting Workflow – Precision Cutting and Polishing of Transparent Gemstones

Faceting is a meticulous process that requires exact control over abrasives, angles, and polish. It typically begins by dopping a clean piece of gemstone rough to a dop stick using wax or adhesive. Using a faceting machine, the gem is first shaped and blocked out with a 260 or 360 grit diamond lap. This step cuts the main facets and defines the pavilion (bottom half) of the stone. For very small or delicate gems, some cutters may skip the coarsest grit and begin with 600 grit to minimize damage.

After blocking, the cutter refines each facet with 600, then 1200 grit laps. These stages remove surface pits and scratches while sharpening facet edges. Once the pavilion is completed, the stone is transferred to the opposite dop, and the crown (top half) is shaped and cut in the same progression.

Next comes pre-polishing, a critical phase for achieving crisp facet edges and clarity. This is typically done with a 3,000 or 8,000 grit diamond compound on a BATT, ceramic, or tin lap, depending on the stone. Some faceters may use aluminum oxide on hard felt for quartz or cerium oxide for beryl or feldspar.

Final polishing varies by material:

• Quartz and amethyst polish well with cerium oxide on a felt lap.

• Beryl, topaz, and feldspar do well with Linde A (aluminum oxide).

• Corundum (sapphire/ruby) often requires 50,000 or 100,000 grit diamond on a ceramic or tin lap to achieve perfect polish.

• Zircon and spinel benefit from 50,000 grit on a BATT or phenolic lap.

The final polish must be done with light pressure, low speeds (typically 200–600 RPM), and a well-conditioned lap surface to prevent scratches, orange peel, or facet rounding. Cleanliness at this stage is critical—one stray grain of grit can ruin hours of work.

📌 Tip: Many experienced faceters keep multiple polishing laps reserved for specific compounds to avoid cross-contamination.

3. Tumbling Workflow – Mass Polishing for Bulk Rough or Beads

Tumbling is a batch process ideal for polishing many stones at once, such as agates, jaspers, and river rock. It involves a series of progressively finer abrasives, typically run over weeks, not hours.

Stage 1: Coarse Grind
Stones are loaded into a rotary or vibratory tumbler with 60/90 or 80 grit silicon carbide, water, and plastic or ceramic filler media to cushion the load. This stage removes sharp edges and shapes the stones. It typically runs for 7–10 days. It’s important to check the barrel periodically to ensure it isn’t leaking or drying out.

Stage 2: Medium Grind
After thoroughly cleaning the stones and barrel, the next stage uses 120 or 220 grit silicon carbide for another 5–7 days. This smooths the stones and eliminates surface pits left by the coarse grind. Again, cleaning between stages is critical.

Stage 3: Fine Grind (Pre-polish)
This stage uses 500 or 600 grit, and begins to give the stones a matte luster. This is a transitional step preparing for final polish. It typically runs for 4–6 days depending on the hardness and quality of the stones.

Stage 4: Polish
The final polish stage uses a polishing compound like cerium oxide, aluminum oxide, or tin oxide. Softer materials may respond better to tin oxide, while quartz-based stones generally polish best with cerium oxide. Add the compound to the barrel with filler media and water, and run for 7–10 days. When done correctly, stones will have a glassy, smooth finish with no scratches or residue.

Some advanced tumblers experiment with diamond grit or paste (3,000–14,000 grit) in the polish stage, especially for harder materials or higher-end jewelry stones. Vibratory tumblers tend to polish faster and are preferred for delicate finishes, while rotary tumblers are better for heavy shaping.

✅ Important: Cleanliness between stages is absolutely vital in tumbling. Even a few leftover grains of coarse grit can ruin the polish stage.