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What Rocks can be tumbled together? Even if you are a beginner or a professional, there is always that curiosity about which rocks can be tumbled together.
Essentially, most rocks can’t be tumbled in a rock tumbler. Choosing rocks of the same family is very important in tumbling. It would be best to determine the Mohs scale hardness of your specimens and assure that they are of the same value. Selecting the right sizes and tumbling rough is also essential when mixing different rocks for tumbling.
With that being said, I will present to you the complete list with tips on what rocks can be tumbled together, why, and how. Read on and enjoy!
If you are interested in checking out the best rock tumbler made by National Geographic you can find it by clicking here (Amazon link).
What Rocks Can Be Tumbled Together
As previously stated, rocks with the same Mohs hardness usually can be tumbled together. However, there are some things to consider, and this is what we will try to cover in this chapter.
The most common tumbled rocks can be split into 12 large groups, according to their Mohs hardness.
The first group belongs to the beautiful chrysocolla, also known as eilatite. This stone has a hardness between 2 and 7, and it should be carefully checked before mixing it with other rocks in the tumbler.
In the second group, we have included the calcites such as blue calcite and orange calcite. Their Mohs hardness is about three and can be safely tumbled together but will require checking from time to time. Marble also has a Mohs hardness of 3.
| Specimen | Mohs Hardness |
|---|---|
| Blue calcite | 3 |
| Orange calcite | 3 |
| Marble | 3 |
The third group is dedicated to the rocks with Mohs hardness between 3.5 and 5.
| Specimen | Mohs Hardness |
|---|---|
| Magnesite | 3.5 |
| Indigo gabbro | 4 – 5 |
| Fluorite | 4 |
| Apatite, Blue Apatite | 5 |
All the above specimens can be safely tumbled together. They are considered soft rocks, and it will take only a few days to bring them to the polishing stage.
The fourth group belongs to the obsidian. We included this rock in a separate category as it is one of the specimens that should be tumbled separately. Obsidian is a fragile rock that splits into sharp chips that might cause bruises if tumbled with other species.
| Specimen | Mohs Hardness |
|---|---|
| Obsidian | 5 – 5.5 |
| Snowflake obsidian | 5 – 5.5 |
| Apache tears | 5 – 5.5 |
Another notable group is the tiger’s eye family of rocks. The best results are obtained if these stones are tumbled together.
| Specimen | Mohs Hardness |
|---|---|
| Tiger’s Eye | 5.5 – 6 |
| Red Tiger’s Eye | 5.5 – 6 |
| Gold Tiger’s Eye | 5.5 – 6 |
The sixth group is composed of rocks with an average of 6.06 Mohs hardness that can be safely tumbled together.
| Specimen | Mohs Hardness |
|---|---|
| Green Opal | 5.5 – 6 |
| Hematite | 5.5 – 6 |
| Rhodonite | 5.5 – 6.5 |
| Amazonite | 6 |
| Labradorite | 6 – 6.5 |
Feldspars have a hardness of 6 – 6.5 and can be tumbled together but will require a longer time.
Group 6 features harder rocks, up to 7 on the Mohs scale.
| Specimen | Mohs Hardness |
|---|---|
| Petrified wood | 6.5 – 7 |
| Jasper | 6.5 – 7 |
| Agate | 7 |
| Carnelian | 7 |
| Quartz | 7 |
| Chalcedony | 7 |
Many specimens of this group are tumbled together. Larger chunks of quartz require a ceramic tumbling media, though. Jasper and agate are recommended for beginners as they have an excellent satisfying luster.
The banded amethyst has a Mohs hardness of 7 and requires separate tumbling due to its fragile nature. The same goes for large specimens of rock quartz, clear quartz, crystal quartz, or rose quartz.
Going up on the Mohs scale, it becomes more challenging to tumble rocks due to their hardness. Diamonds, for example, who are at ten on the Mohs scale, can’t be smoothed as no grit can grind them.
BTW: Do you want to know more about rock and mineral identification? The books listed below are the best ones you can find on the internet (Amazon links):
- Smithsonian Handbooks: Rocks & Minerals
- Gemstone & Crystal Properties (Quick Study Home)
- Ultimate Explorer Field Guide: Rocks and Minerals (National Geographic Kids)
What To Take Into Consideration When Tumbling Different Rocks Together
There are five things to consider when tumbling different rocks together: their Mohs hardness, size, rock family, tumbling rough & grit, and the rocks’ quality.
Once you learn how to pick the right rocks for tumbling, there is nothing that can stop you from turning rough stones into stunning shiny gems.
Rock Quality
The quality of your rock specimens is critical when it comes to tumbling. Voids and pore spaces can ruin the tumbling process – the rocks will have coarse-grit scratches.
The rocks you want to polish must be free of fractures. These tiny crackings will cause rocks to split into little parts that will scratch the polished stones.
Lastly, the rocks you want to polish must have a smooth texture; otherwise, the granular debris that they produce will scratch the other stones in the tumbler’s barrel.
TIP: Rock tumbling can be quite time-consuming. That’s why is always good to know how long tumbling takes for various rocks and minerals. Find out more in the article below:
How Long Does It Take To Tumble Rocks? Values For Various Rocks
Mohs Scale Hardness
Each specimen has a hardness level, generally measured upon the Mohs hardness scale. When tumbling different rocks together, their hardness should be on the same level.
Anything below seven on the Mohs scale is considered a soft material. You can measure a rock’s hardness by using a Mohs Test Kit (available online).
Another method would be to scratch the rock’s surface with an object of a certain hardness such as your fingernail, a copper penny (new pennies are made of zinc, so try to find an old copper coin), obsidian, knife blade, steel file, or a piece of quartz.
| Object | Mohs Hardness |
|---|---|
| Fingernail | 2.5 |
| Copper Penny | 3.5 |
| Obsidian | 5 |
| Knife Blade | 5.5 |
| Steel File | 6.5 |
| Quartz | 7 |
If the object you use is scratching the rock, you know the hardness of that particular stone.
Any rock with a hardness of 5 to 7 will take a nice polish. Harder rocks will display a gloss finish, while softer stones will get smooth and rounded but with no polish.
TIP: If you are interested in buying a Mohs hardness test kit, I wrote an article about the best 3 Mohs test kits where you will find all the information you need before the purchase. Find out more in the article below:
3 Best Mohs Scale Test Kits: Test Hardness of Your Gemstones
Size
Size is also significant when it comes to tumbling. It also affects the time in which your stones are done tumbling.
If you try to tumble specimens of the same size, the whole process will last longer, and the results will not be satisfying.
As a general rule, always have in mind the size of your tumbler, and make sure you choose rocks of different sizes. Larger specimens require an extended tumbling time, so it is better to avoid them. If you want to find out more about how long tumbling takes, check it here.
Rock Family
Probably the safest way without getting any tool kits to tumble different rocks together is to make sure they are of the same family. For example, blue calcite and orange calcite go well together, they have the same hardness levels.
Another example is the obsidian family, which includes regular obsidian, snowflake obsidian, and apache tears.
Tumbling Rough & Grit
Even if you are an amateur or professional, you may not find rocks in the area where you’re living. But this is not an issue, and you can still tumble rocks. All you need to do is to purchase some tumbling rough.
Moreover, even if collecting rocks can be fun, it is more economical to purchase the tumbling rough. In case you want to tumble a specific material such as malachite or lapis lazuli, buying the specific tumbling rough is more comfortable than waiting until you collect a fair amount of rocks.
Grit is also very important in rock tumbling, and you should choose the right one for your specimens. Silicone carbide grit, for example, has a Mohs hardness level of 9, and it works excellent with jasper, for instance.
Choosing the Right Tumbling Rocks
Tumbling rocks takes a lot of time, patience, and electricity. It is essential to choose the right rough material.
Some of the rocks that are commonly tumbled nicely are jasper, agate, moonstone, laps lazuli, obsidian, petrified wood, amethyst, tiger’s eye, or other varieties of quartz.
However, not every type of rock is suitable for tumbling. As a beginner, it is better to stick to quartz and agates.
A useful piece of advice is to use rocks of the same hardness. As for the size, although it is recommendable to tumble rocks of different sizes, try to avoid the stones that are too big (over 3 inches).
The rocks you are about to toss into the tumbler should not have deep cracks or voids. The unusually shaped stones are also a no.
TIP: As already stated above, not all rocks are good for tumbling. That is the reason I summarized the list of the best 15 rocks for tumbling. Check out the best rocks for tumbling below:
What Rocks Are Good For Tumbling? 15 Best Rocks & Minerals
Can I Tumble River Rocks?
River rocks can be tumbled, and the results are amazing. Polished river rocks are used in home decorating or as massage stones.
Tumbling these stones, though, takes a long time that is determined by the rocks’ hardness.
The tumbling process requires a standard rock tumbler. The stones can also be altered to your preference by alternating the grit’s size and the duration of tumbles.
Conclusion
Collecting rocks is a cool way to spend your free time. Tumbling the rocks you gathered is even better since you can discover their inner beauty.
However, it is essential to learn some basics before tossing the stones into a tumbler. The results will be more satisfying.
In general, rocks of similar hardness can be tumbled together. Some, though, require special attention and extra tumbling time.
Rock tumbling is a beautiful hobby, and once you master it, you will gain a new appreciation for the beauty of the natural world.
TIP: You know what rocks can be tumbled together. But do you have idea what to do with tumbled rocks? Check out these simple and clever ideas in the article below:
What Can You Do with Tumbled Rocks? 10 Simple & Clever Ideas