Material compatibility guide
Rock Tumbling Compatibility Chart: What Rocks Can Be Tumbled Together?
Match hardness, toughness, texture and stage requirements—not color alone—to build batches that grind evenly without sacrificing softer or more fragile stones.
Rock tumbling compatibility chart
Use this chart as a conservative starting point. A material name does not guarantee identical behavior: weathering, fractures, inclusions, porosity and locality can change how two pieces survive a tumbler. When identification is uncertain, test a small batch rather than risking your best rough.
| Material | Approx. Mohs hardness | Tumbling behavior | Good starting companions | Main caution |
|---|---|---|---|---|
| Agate | 6.5–7 | Hard, tough chalcedony; excellent polish potential | Jasper, chalcedony, chert/flint, fully silicified petrified wood | Deep fractures and druzy cavities can trap grit |
| Jasper | 6.5–7 | Usually tough and beginner-friendly | Agate, chalcedony, chert/flint, compatible petrified wood | Soft seams or porous varieties can shed material |
| Chalcedony | 6.5–7 | Fine-grained quartz family; generally durable | Agate, jasper, chert/flint | Thin or highly fractured pieces may chip |
| Chert / flint | About 7 | Dense and usually tough | Agate, jasper, chalcedony | Sharp broken edges need enough coarse-stage time |
| Petrified wood | Often near 7 when fully silicified | Can tumble like chalcedony when mineralization is complete | Agate, jasper, chalcedony | Soft wood-like zones, voids or mixed mineralization may undercut |
| Massive quartz | 7 | Hard but more prone to edge bruising than many jaspers | Other sound quartz; cautious batches with hard chalcedony | Use media and avoid loose, high-impact loads |
| Rose quartz | 7 | Hard crystalline quartz; can take a bright polish | Rose quartz or similar quartz with cushioning | Edge bruising; needs gentler movement and media |
| Amethyst / crystal quartz | 7 | Hard, but crystal pieces can chip and lose natural faces | Similar massive quartz if you actually want rounded stones | Do not tumble collectible crystal points you want to preserve |
| Aventurine | About 6.5–7 | Quartz-rich, usually workable | Similar durable quartz-family material | Inclusions can create pits or uneven wear |
| Tiger’s-eye | About 6.5–7 | Quartz-rich and polishable | Similar tough quartz-family material | Fractured or fibrous-looking zones deserve inspection |
| Unakite | Roughly 6–7 | Mixed-mineral rock; often tumbles well | Best with similar unakite or carefully matched material | Different minerals can wear at different rates |
| Granite | Roughly 6–7 overall | Mixed minerals with different cleavage and wear | Similar granite from the same source | Feldspar and mica can undercut or bruise; not equivalent to agate |
| Labradorite | About 6–6.5 | Feldspar; can polish but has cleavage | Prefer a dedicated batch | Edges can cleave or chip; protect flash-bearing faces |
| Sodalite | About 5.5–6 | Softer than common quartz-family rough | Dedicated sodalite batch | Harder stones can scratch or consume it quickly |
| Obsidian | About 5–5.5 | Natural glass; soft enough to shape fast but brittle | Obsidian / Apache tears with generous cushioning | Separate from agate, jasper and quartz; chips and bruises easily |
| Lapis lazuli | Variable, often about 5–5.5 | Composite rock with variable minerals | Dedicated, carefully sorted batch | Soft calcite-rich zones can undercut |
| Turquoise | About 5–6 | Relatively soft and often porous | Dedicated special-method batch | Can lose material rapidly and may not tolerate standard recipes |
| Fluorite | 4 | Soft with perfect cleavage | Dedicated advanced batch only | Standard agate-style tumbling is too aggressive |
| Calcite / marble | About 3 | Very soft compared with quartz-family material | Dedicated soft-stone method | Rapid wear; standard hard-rock schedule can destroy the load |
Mohs values are approximate and describe scratch resistance, not toughness. A rock can be hard yet brittle, or relatively soft yet mechanically durable. Always inspect the actual pieces in front of you.
Four tests matter more than matching a number
1. Hardness
A large hardness difference usually means the harder material will scratch and outlast the softer material. For a mixed beginner batch, close hardness is a good first filter.
2. Toughness and fracture
Obsidian and crystalline quartz illustrate why hardness is incomplete. They can be hard enough to polish yet still bruise or chip when the load is too violent.
3. Texture and porosity
Granular or porous pieces can shed particles during later stages. One shedding stone can contaminate an otherwise clean polish batch.
4. Condition
Fresh fractures, open seams and unstable edges can make two normally compatible materials a bad pairing. Sort the pieces, not only the labels.
A simple compatibility decision
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When a mixed batch is worth the risk
A mixed batch is useful when the materials are genuinely compatible and the variety helps create a better size distribution. Agate, jasper, chalcedony and fully silicified petrified wood are classic examples because they are usually hard, fine-grained and durable. Even then, remove pieces with open fractures, soft seams or gritty surfaces before they enter fine and polish stages.
When to separate material even if hardness matches
Crystalline quartz and agate can both measure around Mohs 7, but quartz often bruises more readily. Granite may fall in a similar overall hardness range, yet its feldspar, quartz and mica grains do not wear like homogeneous chalcedony. Treat matching Mohs numbers as permission to investigate further—not as proof that the rocks belong together.
Use the compatibility checker before building the load
The free Rock Tumbling Compatibility Checker gives conservative starting guidance for common materials. It is designed to flag obvious mismatches and direct you to a material-specific guide, not to replace identification or a small test batch.
Questions people ask before mixing rocks
Can agate and jasper be tumbled together?
Usually, yes, when both are sound, dense material with similar size and condition. They are among the most forgiving hard materials for a beginner batch.
Can quartz be mixed with agate?
Sometimes, but use more caution than the hardness number suggests. Quartz can bruise at the edges, especially in a loose load. A quartz-only batch with ceramic cushioning is safer when the pieces are large, clear or valuable.
Can obsidian be tumbled with quartz or agate?
Do not treat them as a normal mixed batch. Obsidian is softer and much more brittle, so harder stones can turn a promising obsidian load into chips and cloudy impact marks.
Can beach rocks all go in one barrel?
No. “Beach rock” describes where a pebble was found, not what it is made of. Sort mixed beach stones by texture, hardness, visible fractures and likely composition before loading them together.