Rock Discoveries

Rock Tumbling 101: How to Choose the Best Rocks for Polishing

Rock tumbling is a fun hobby for geology enthusiasts of all ages. The process of tumbling rocks involves using a tumbler to polish and shape various types of gemstones, rocks, and minerals.

However, one crucial aspect of rock tumbling is choosing the right rocks for the tumbler. When selecting rocks for a tumbler, hardness is an essential factor to consider.

Rocks with a high level of hardness are ideal for tumbling because they are more abrasion-resistant, which means that they will not break or scratch easily. The Mohs hardness scale is a system that measures the hardness of minerals and rocks.

The scale ranges from 1 to 10, with 1 being the softest and 10 being the hardest. The Mohs hardness scale is the gold standard when it comes to selecting rocks for a tumbler.

It is a scientific system that measures the resistance a mineral or rock has to scratching and abrasion. The scale ranges from 1 to 10, with 1 being the softest and 10 being the hardest.

The ideal hardness range for rocks that are suitable for tumbling is between 7 and 9. Rocks with a hardness level below 7 are not recommended for tumbling because they are too soft.

Soft rocks will not tumbled as effectively as harder rocks, and the process may result in scratches, dullness, or outright breakage. Conversely, rocks that are too hard are difficult to polish, resulting in a longer tumbling time and increased wear and tear on the tumbler’s motor and bearings.

When selecting rocks for tumbling, it is important to identify the rocks’ hardness level to ensure that they are suitable for the tumbler. Here are some popular rocks and where they fall on the Mohs hardness scale:


Talc – 1 (too soft for tumbling)

2. Gypsum – 2 (too soft for tumbling)


Calcite – 3 (too soft for tumbling)

4. Fluorite – 4 (too soft for tumbling)


Apatite – 5 (too soft for tumbling)

6. Orthoclase Feldspar – 6 (too soft for tumbling)


Quartz – 7 (ideal for tumbling)

8. Topaz – 8 (ideal for tumbling)


Corundum – 9 (ideal for tumbling)

10. Diamond – 10 (too hard for tumbling)

It is also necessary to note that some rocks and minerals are not suitable for tumbling due to their physical properties.

For example, rocks that are porous, brittle, or have a high water content may not withstand the tumbling process. Other rocks that should be avoided include those with metallic luster, as they can damage the tumbler’s barrel.

Soft rocks can also pose a challenge when it comes to polishing, as they may require more extended tumbling times than harder rocks. This can put a lot of stress on the tumbler’s motor and bearings, leading to wear and tear over time.

Conversely, hard rocks may not require as much tumbling, but polishing them can be a more challenging task, requiring more time and patience. In conclusion, selecting the right rocks for your rock tumbler is an essential part of the tumbling process.

Understanding the Mohs hardness scale, along with other physical properties of rocks and minerals, can help you make informed decisions when choosing materials to tumble. By paying attention to the hardness of the rocks, you can ensure that your tumbler functions correctly and your tumbled rocks come out polished and beautiful.

When it comes to rock tumbling, selecting the right rocks for the process is crucial. Not all rocks are suitable for tumbling, and, in fact, some rocks may work against the process instead of enhancing it.

In this article, we will discuss what characteristics to look for in rocks that make them ideal for tumbling, as well as provide examples of good rocks for tumbling. One of the most essential characteristics of rocks suitable for tumbling is hardness, as explained in the previous section.

In addition, other characteristics that contribute to good rocks for tumbling include density, pore-freeness, and smooth texture.


When it comes to rock tumbling, ideal rocks are usually denser rocks, such as quartz, which is one of the most popular gemstones for tumbling. The higher the density, the smoother the finish of the tumbled stone.

Heavier rock types also provide more significant momentum, which helps to polish the rock’s surface. A rock’s density depends on its composition and how tightly packed its mineral grains are.


Pores in rocks can be detrimental to the tumbling process. Porous stones can trap abrasive materials and grit between their pores, which can damage the tumbling barrel and lead to a slower and less effective polishing process.

Therefore, solid and dense rock types are better suited for rock tumbling because they are less porous and do not trap grit within their structure.

Smooth texture

The texture of a rock’s surface can impact how well it gets polished in a rock tumbler.

Smooth textured rocks, which are free of rough bumps and fissures, are ideal for tumbling.

This is because the surface is less likely to snag on other rocks during the tumbling process, potentially resulting in cracks or breaks. Additionally, smooth-textured rocks allow for a more even distribution of grit during tumbling, which leads to a smoother and polished surface.

Fractures and Cracks

Fractures and cracks are harmful to the tumbling process and can cause the rock to break down more quickly. Fractures can also trap abrasive materials and grit, which leads to much slower and ineffective tumbling.

It is essential to avoid rocks with visible cracks and fractures during the selection process.

Examples of Good Rocks for Tumbling

Now that we have discussed what characteristics make good rocks for tumbling, let us explore some examples of rocks that are highly recommended for rock tumbling. 1.

Quartz – Quartz is a widely popular rock type for rock tumbling because it is denser and highly resistant to abrasions. This rock type comes in various colors and sizes and is incredibly versatile in applications.

2. Agate – Agate is a chalcedony mineral that is an excellent option for rock tumbling because it is non-porous and comes in various colors.

It has a smooth texture that ensures that it tumbles evenly, minimizing the chances of cracks and other imperfections. 3.

Jasper – Jasper is a dense, smooth, and non-porous rock type that tumbles exceptionally well and comes in a wide range of colors. It is ideal for making smaller decorative items.

4. Carnelian – Carnelian is a translucent orange-colored rock type that is highly popular for rock tumbling.

It is dense and has a smooth texture and a non-porous structure, allowing for fast and efficient polishing. 5.

Labradorite – Labradorite is a feldspar mineral that humbles very well and can produce iridescent tumbled stones. It has a smooth surface and a non-porous structure, making it a great choice for rock tumbling.

In conclusion, selecting the right rocks for tumbling is crucial if you want to achieve polished, beautiful stones. It is necessary to opt for dense, non-porous, and smooth textured rocks while avoiding rocks with cracks and fractures.

We hope that the above information helps you select the best rocks for tumbling and ensures that your stones come out polished and stunning. In conclusion, choosing the right rocks for rock tumbling is crucial to achieving the desired results.

Rocks with a hardness between 7-9 on the Mohs scale, a high density, non-porous surface, and smooth texture are highly recommended for effective tumbling. Avoiding rocks with fractures and cracks is also essential.

By following these tips, geology enthusiasts can enjoy the process of rock tumbling and create beautiful stones to add to their collections. FAQs:


Can any rock be tumbled? No, not every rock is suitable for tumbling.

It is essential to select rocks with the right hardness, density, and texture to have a successful tumbling process. 2.

What should I avoid when selecting rocks for tumbling? Rocks with fractures and cracks, porous surfaces, metallic luster, and soft rocks with a Mohs hardness level less than 7 should be avoided.

3. Can I tumble rocks of different hardness levels together?

It is not recommended to tumble rocks with vastly different hardness levels together, as the softer rocks will wear down much quicker than harder rocks. 4.

Why is selecting the right rock important for tumbling? Selecting the right rock type can significantly impact the effectiveness and finish of the tumbling process, leading to either desirable or undesirable results.

5. Should I wash the rocks before tumbling them?

Yes, it is essential to wash the rocks before tumbling them, as any dirt or debris can damage the tumbling machine and the rocks inside.

Popular Posts