Polishing Labradorite in a Rock Tumbler

What is Labradorite?

Labradorite belongs to the plagioclase feldspars. The familiar colour flash is not a pigment on the surface; it is caused by light interference in very thin internal layers. As a result, the same piece can glow an intense blue from one angle and look fairly grey from another. The orientation of a stone therefore has a major effect on the visual result.

Is this stone suitable for a rock tumbler?

Labradorite can be tumbled in a rock tumbler, but it is not an ideal stone for beginners. Because of its distinct cleavage and slightly lower hardness, it is more prone to chipping than chalcedony or quartz. Preferably use a separate batch with similar stones, plenty of ceramic media and a well-filled barrel.

It is better not to mix labradorite with much harder agate or quartz if you want to limit damage. A separate batch of labradorite is safest. Ceramic media help support the stones, fill the space and reduce hard impacts.

• Preferably make a separate labradorite batch.
• Use plenty of ceramic media.
• Avoid a half-empty barrel; the stones will hit each other harder.
• Check regularly for new chips or broken splinters.
• Assess the colour flash in both dry and wet light from different angles.

Step-by-step polishing

The exact tumbling time depends on how rough your stones are, the barrel and how much material you want to remove. So do not rely on the calendar alone: inspect the stones after each stage for shape, scratches and cracks. The general process is explained in more detail in our step-by-step stone polishing guide.

Practical tip: Only move on to a finer grit when the result of the current stage is truly good. A scratch, pit or sharp edge left in stage 1 will not disappear by itself during the polishing stage.

Which grit and tools do you need?

For most hard tumbling stones, a progression from coarse to ever finer silicon carbide works best, followed by a true polishing stage. See the current range of grit and polishing materials. Ceramic media can help fill the barrel properly, distribute the slurry and reduce hard impacts between stones.

Common problems

Which stones can you combine it with?

It is better not to mix labradorite with much harder agate or quartz if you want to limit damage. A separate batch of labradorite is safest. Ceramic media help support the stones, fill the space and reduce hard impacts.

Hardness is important, but it is not the only criterion. Brittleness, existing fractures and porosity also determine whether stones make a good batch together. Unsure? A separate batch is almost always safer than combining very different materials.

How do you recognise good rough pieces for the tumbler?

Do not look at colour alone. For a good tumbling result, compact, sturdy pieces are usually the most suitable. Avoid material that crumbles under light pressure, has very thin protrusions or is full of deep open cracks. Such areas can break off or trap coarse grit.