Polishing Hematite in a Rock Tumbler
Polishing Hematite in a Rock Tumbler
Hematite is an iron oxide that can take on a striking steel-grey to almost mirror-like metallic lustre after polishing. The stone feels relatively heavy and looks completely different from quartz or jasper. In a rock tumbler, hematite can turn out beautifully, but it does require a different approach.
Hematite is an iron oxide that can take on a striking steel-grey to almost mirror-like metallic lustre after polishing. The stone feels relatively heavy and looks completely different from quartz or jasper. In a rock tumbler, hematite can turn out beautifully, but it does require a different approach.
What is Hematite?
Hematite consists mainly of iron oxide. Rough material can be dull grey, black, reddish brown or metallic. A striking feature is the reddish-brown streak of natural hematite, even when the surface itself appears almost black or silver-grey.
Hardness
The hardness is around about 5.5 to 6.5. That tells you a lot about which stones you can safely combine.
Suitable for the rock tumbler?
Compact natural hematite can be tumbled and become very shiny. The material is heavy and can hit other stones quite firmly. For that reason, using it in a separate batch or only with similarly hard material is sensible. Also watch out for imitation or artificially made ‘hematite’ on the market; it does not always behave the same way.
Can Hematite go in a rock tumbler?
Compact natural hematite can be tumbled and become very shiny. The material is heavy and can hit other stones quite firmly. For that reason, using it in a separate batch or only with similarly hard material is sensible. Also watch out for imitation or artificially made ‘hematite’ on the market; it does not always behave the same way.
It is best to tumble hematite separately. Because of its high specific gravity and metallic structure, it can put a different load on other stones than a normal quartz mix.
- Preferably run hematite in its own batch.
- Use enough smaller pieces or suitable media to cushion movement.
- Check the barrel more often for sharp broken fragments.
- Clean the barrel completely before the final stages.
- Expect the slurry to turn dark because of the iron-rich material.
Polishing Hematite: step by step
Never rely on time alone; inspect the surface after each stage. A stone that still has sharp edges, deep pits or obvious scratches is usually not ready for the next grit yet. You can also find the general process in our stone polishing step-by-step guide.
Check that the material is compact
Avoid highly flaky or crumbly pieces that may fall apart while tumbling.
Fill the barrel properly
Because hematite is so heavy, hard impacts are especially undesirable.
Work carefully down to fine grit
Small scratches stand out quickly on a metallic-lustre surface.
Polish cleanly
Good pre-polishing and thorough cleaning are essential for the final metallic lustre.
Important: clean the barrel, lid, rim, stones and media thoroughly before moving to a finer grit stage. A few coarse grains left behind can cause new scratches in a later stage.
Which grit should you use?
For many tumbler stones, a progression from coarse silicon carbide to increasingly finer grits, followed by a pre-polish and polish stage, works well. The run time needed depends on the stone, the starting shape and how much material you want to remove. See the current range of grit and polishing media.
Coarse grit shapes the stone
The first step is intended to round sharp edges, remove weathered outer layers and grind away small irregularities.
Fine grit prepares for shine
The final grinding stages remove the scratches from the previous grit. Polishing compound only works really well once the surface is completely smooth.
Which stones can you combine it with?
It is best to tumble hematite separately. Because of its high specific gravity and metallic structure, it can put a different load on other stones than a normal quartz mix.
Hardness is not the only criterion. Brittleness, cleavage, porosity and existing fractures are at least as important. Two stones can be roughly the same hardness and still react very differently in the same barrel. If in doubt, a separate batch is safer.
Common problems
| Problem | Likely cause and solution |
|---|---|
| Many fine scratches | The metallic lustre makes scratches extra visible. Check for contamination and sharp splinters. |
| Stones collide hard | Hematite is heavy; make sure the barrel is sufficiently full and the batch runs smoothly. |
| Material crumbles | Not all hematite is compact enough for tumbling. Flaky or porous pieces are better kept separate. |
How do you recognise good rough material?
The quality of the rough stone determines a large part of the final result. Prefer compact pieces without deep open cracks, loose crust or strongly granular areas. Porous stones can hold grit and crumbly pieces can produce sharp fragments that scratch other stones.
Suitable
Solid, compact, no loose crust, no deep open cracks and a size that fits well in the barrel.
Less suitable
Very thin projections, porous areas, soft weathered skin and cracks that are already almost open.
Polish stones yourself?
With a good rock tumbler, enough fill and the right grit, you have the most control over the result. Take your time especially in the coarse stage: what is not corrected there will usually still show later.
Frequently asked questions about Hematite
Can hematite go in a rock tumbler?
Yes, if it is compact natural hematite. A separate batch is usually the wisest choice.
Why does hematite feel so heavy?
Hematite has a high density because of its large iron oxide content.
Is hematite magnetic?
Pure hematite is not strongly magnetic. Strongly magnetic ‘hematite’ may be a different or artificial material.
Can hematite be tumbled with jasper?
It can, but because of the high weight, tumbling it separately is usually safer.