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Identifying, choosing and polishing stones

Rock types for a rock tumbler

Not every rock type behaves the same in a rock tumbler or polishing tumbler. Some stones become smooth and glossy relatively easily, while other types are softer, more porous or more prone to breaking.

On this page you will find an overview of the rock types for which RockTumbler.nl information is available, with attention to properties, hardness and tumbling and polishing the stone.

Which stones are suitable? Browse rough stones

When choosing stones for a polishing tumbler, people often first look at the Mohs hardness scale. That is important, but hardness alone does not determine whether a stone is suitable for tumbling.

The structure of the stone also plays a major role. A hard stone with many cracks, soft inclusions or a porous surface can still cause problems during tumbling. A compact and uniform stone is usually easier to process.

It is therefore sensible to tumble stones with roughly the same properties together. Large differences in hardness can cause softer stones to wear much faster or become damaged.

What should you look for in a rock type?

For a good result, these three properties are especially important.

Hardness

Many popular tumbling stones are around Mohs 6 to 7. Think of many types of quartz, agate and jasper. Stones with very different hardness are usually best not combined in the same batch.

Structure

Compact stones without deep cracks are usually easier to polish. Porous, brittle or heavily cracked stones can retain grit, chip away or cause new scratches during later stages.

Polishability

Not every stone achieves the same high gloss. Some rock types can become mirror-smooth, while others naturally retain a softer or more silky sheen.

Mohs hardness is a guideline, not a guarantee. Two stones with roughly the same hardness can still behave very differently because of differences in structure, cracks, porosity or composition. So always assess the stone itself, not just the number on the Mohs scale.

Which rock types are suitable for beginners?

For a first batch, hard and compact stones are usually the easiest. Agate, jasper, carnelian, tiger’s eye and many quartz-like stones are therefore popular choices for a rotary rock tumbler.

Softer or more delicate types can also turn out beautifully, but they often require more attention to barrel fill, tumbling time, the combination of stones and the grit used.

Do you mainly want to know which stones you can and cannot tumble together? Then view the detailed selection guide Which rocks are suitable for a rock tumbler?

All rock types from A to Z

Below you will find all rock types for which RockTumbler.nl information is available. Choose a rock type for more information about properties, hardness, identification and points to watch during grinding and polishing in a rock tumbler.

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