Rock Tumbling Grit Guide: Which Grits, How Much, and When

The grit is where most beginners go wrong. They buy a tumbler, find some rocks, and then guess at grit amounts or skip stages because the process seems slow. The result: dull, scratched stones after 4 weeks of running.

This guide covers exactly which grits to use, how much, when to move on, and what to do when things go wrong. For more on the tumbling process itself, see our complete step-by-step rock tumbling guide.

Grit Stages at a Glance

Stage 1: Coarse Grinding (60/90)

This is the heavy work. 60/90 silicon carbide is aggressive — it removes material fast, rounds sharp edges, and works through surface fractures. Expect to lose 10–20% of rock volume in this stage, especially with fractured or rough specimens.

• Fill barrel 2/3 to 3/4 full with rocks of similar hardness
• Add 2 tablespoons of 60/90 per pound of rock
• Add water until it just covers the rocks
• Run 7 days, then check: stones should be smooth and rounded with no sharp points remaining
• If stones still have sharp spots or flat faces, run another 3–5 days

Don't move to Stage 2 until stones are fully rounded. Rushing Stage 1 produces faceted stones with persistent flat spots that never polish out.

Stage 2: Medium Grinding (150/220)

Stage 2 removes the coarse scratches left by Stage 1. After a proper Stage 2, stones should look smooth and matte when dry, and slightly shiny when wet. The surface should feel smooth to the touch with no grittiness.

• Clean all stones, the barrel, and the lid thoroughly — any 60/90 contamination ruins this stage
• Add 2 tablespoons of 150/220 per pound of rock
• Run 7 days minimum
• Check: stones should have no visible scratches under normal light when wet

The cleaning step between stages is where most contamination happens. Use separate buckets for washing, and don't wash any Stage 1 or Stage 2 tools in the same sink as your Stage 3/4 supplies.

Stage 3: Pre-Polish (500 / TXP)

Pre-polish is the bridge between grinding and shining. Stones going into Stage 3 should look matte. Stones coming out should have a faint, milky luster when wet. If there's no shine developing, Stage 2 didn't fully complete.

• Clean everything again — same protocol as between Stages 1 and 2
• Add 500 grit silicon carbide or TXP pre-polish compound
• Some tumblers use plastic pellets in Stage 3 to cushion the load — follow your machine's instructions
• Run 7–10 days

Stage 4: Polish (Cerium Oxide / TXP Polish)

The final stage produces the mirror finish. Use Cerium Oxide for quartz-family stones (agate, jasper, quartz). Use aluminum oxide for softer stones. TXP (Lortone's pre-polish/polish compound) works across most rock types.

• The polish stage barrel should be spotlessly clean — no grit of any kind
• Add plastic pellets to fill the barrel to 2/3–3/4 full (they cushion stones and prevent flat spots)
• Use 1–2 tablespoons of polish per pound of rock (less than grit stages)
• Run 7–10 days
• Remove and rinse: stones should be bright and glassy

Troubleshooting Common Grit Problems

• Stones are dull after polishing: Most likely cause is grit contamination in Stage 4. Rewash everything and re-run Stage 4 with fresh polish.
• Stones have flat spots: Barrel was underfilled. Add more rocks or plastic pellets to bring it to 2/3–3/4 full.
• Stones are pitted: Rock was too fractured or porous. Some material simply won't take a polish regardless of grit sequence.
• Stones lost a lot of volume: Normal in Stage 1 for fractured rough. Use larger starting rough if you want larger finished stones.
• Barrel leaks: Gasket is worn. Replace before running another stage — a leak lets grit and slurry escape and ruins the batch.

Knowing which rocks actually tumble well avoids many of these problems upfront. Our mineral identification guide includes hardness and luster data for common collectible minerals — use it to predict how a specimen will perform before committing it to a batch.

If you're still deciding which tumbler to buy, our rock tumbler buying guide covers the machines best suited to different batch sizes and experience levels. Not sure what to put in the barrel? Our guide to the best rocks for tumbling covers hardness thresholds, which types polish best, and where to source quality rough.

Frequently Asked Questions

What grit sequence should I use for rock tumbling?

The standard 4-stage sequence: Stage 1 — 60/90 coarse silicon carbide (7–10 days), Stage 2 — 150/220 medium silicon carbide (7–10 days), Stage 3 — 500 pre-polish or TXP (7–10 days), Stage 4 — Cerium Oxide or aluminum oxide polish (7–10 days). Clean the barrel and all stones thoroughly between each stage to prevent contamination.

How much grit do I use per batch?

Approximately 2 tablespoons of grit per pound of rock for silicon carbide stages. For the polish stage, use 1–2 tablespoons per pound. Too much grit wastes material; too little produces poor results. The barrel should be 2/3 to 3/4 full of rocks plus water.

Can I reuse grit?

No. Silicon carbide grit breaks down during tumbling into finer particles. Reusing spent grit from Stage 1 in Stage 2 contaminates the batch with coarser particles and produces scratched stones. Always use fresh grit for each stage and each batch.

Why are my stones not shiny after polishing?

The most common causes: contamination from previous grit stages (not cleaning thoroughly between stages), skipping the pre-polish stage, using the wrong polish for the rock type, or stones too soft to polish (below Mohs 6). Make sure the barrel, rocks, and pellets are completely clean before the polish stage.

Keep Reading

• Rock tumbling step-by-step — complete process walkthrough with stage timing and troubleshooting
• Best rocks to tumble — which rock types match which grit sequences and produce the best finish
• Best rock tumblers 2026 — barrel capacity and motor specs that affect your grit load calculations