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If you’re an avid collector of stones and minerals like calcite, you are probably familiar with the tumbling process. Putting stones through a tumbling machine will make them smooth and shiny, and it’s the perfect way to showcase that stone’s beautiful colors and patterns. But can any stone be tumbled? What about calcite?
Calcite is a very soft stone. This means that putting it through a tumbler could cause it to chip away too quickly before ever getting a beautiful shine to it. But calcite can be tumbled and polished with careful management.
While calcite can’t be tossed into the tumbler with the rest of your stones, there are other ways to get calcite with a nice, smooth finish. It will take extra care, patience, and materials, but it is possible. If you want your calcite to be sleek and shiny like the other minerals, keep reading to find out how.
If you want to check out the best calcite crystals for tumbling, you can find them by clicking here (Amazon link).
Calcite is Soft and Must Be Tumbled Carefully
Not all stones are equally hard. In fact, some stones are actually quite soft. It probably sounds strange to call a rock “soft,” but all stones and minerals have different hardness levels. That means that some rocks are harder to break than others.
Softer rocks, like calcite, might erode away easily in your hand just from rubbing it in your fingers, while others would need to be hit pretty hard to make a chip. Calcite is on the low end of the hardness scale, which we’ll discuss in more detail below.
Minerals and stones are measured on a specific scientific scale to gauge their hardness relative to each other. This helps people categorize the stones and helps collectors who tumble stones as a hobby.
Knowing the hardness of a stone will help you make better decisions about how to polish a stone and what to expect when it comes out of the tumbler.
Mohs Hardness Scale
What is hardness anyway? Aren’t all rocks hard? Rocks come in a range of different hardness levels.
Hardness is measured by the resistance of an object to being scratched. For example, diamonds are famous for being one of the hardest materials ever.
If you tried to scratch a diamond with glass, the glass would be scratched, not the diamond. However, if you scratched a softer stone like marble, the glass would leave a mark on the marble.
There are a few important things to know about the Mohs Hardness Scale:
- The scale determines the hardness of minerals relative to each other
- The scale is a range of values from one to ten
- You can determine the hardness of an unknown mineral by scratching it with other minerals
- The hardest is ten, and the softest is one.
Knowing the hardness of a mineral can be very beneficial when tumbling. To better understand the different hardness values of various materials, refer to this chart:
| Mineral | Value on the Mohs Hardness Scale |
|---|---|
| Talc | 1 |
| Calcite | 3 |
| Marble | 3 |
| Turquoise | 5 to 6 |
| Quartz | 7 |
| Jasper | 7 |
| Diamond | 10 |
TIP: If you want to know the Mohs hardness scale of your rocks and minerals, check out the best Mohs scale test kits in the article below:
3 Best Mohs Scale Test Kits: Test the Hardness of Your Gemstones
How Hardness Affects Rock Tumbling
Typical rock-tumbling instructions tell you to tumble your stones for weeks at a time. Most will tell you to tumble for a full week on each level of grit.
The three levels of grit are:
- Coarse grit
- Medium grit
- Fine grit
Coarse grit takes off the larger jagged pieces of the stones. The medium and fine are meant to take the minerals to a smooth finish and shiny polish.
This longer process of tumbling, taking a week on each level of grit, works well for minerals like agate, jasper, or quartz, which all have seven hardness.
However, softer stones like calcite would not survive tumbling for weeks at a time. Knowing the hardness of a stone will help you more accurately determine the best length of time for tumbling. A softer material like turquoise would do much better with a shorter time tumbling.
The common solution for this is to tumble the same number of days as the mineral’s Mohs hardness value. For example:
- Quartz can be tumbled seven days at a time
- Turquoise five days at a time
- Calcite 3 days at a time
TIP: Did you know you can also use sand for rock tumbling? I wrote an article about when and how to use sand when tumbling rocks. You may find this article helpful; read it here:
Can You Tumble Rocks with Sand? Everything You Need to Know
How to Tumble Calcite
Generally, tumbling calcite isn’t necessary because even rough, it shows the mineral properties and markings. However, polishing calcite will give you that beautiful finish if you want a smooth and shiny stone.
When tumbling calcite, it is important to tumble it only with other stones of the same hardness. This goes for all minerals and stones as well.
Professional rock tumblers agree that it is best not to mix rock types in one load. You should always separate rocks before tumbling.
Here’s what can happen if you tumble rocks of different hardness together:
- Smaller and more irregular rock pieces
- Inconsistent levels of shine and smoothness
- More time spent with the tumbler running
- More wear and tear on your tumbling equipment
Besides keeping your calcite separate, some special tools and techniques will help you get the best results. Keep reading below to learn how to maximize your calcite tumbling.
Dry Tumbling
Stones are usually tumbled in water, but it is best to tumble dry for a stone as soft as calcite. If you use water, you risk eroding more of the stone and quickly reducing your rocks to pebbles.
Here are the steps to dry tumbling:
- Load tumbler with calcite and coarse grit
- Tumble for around three days, checking after each day to ensure the rocks are not breaking apart too much.
- Wash the barrel and calcite.
- Put the calcite back into the barrel along with medium grit and buffering agent to account for the volume lost from the eroded rock.
- Tumble for another 2 to 3 days (checking the tumbler frequently in between)
- Wash the barrel, calcite, and buffering agent.
- Put the calcite back into the barrel with a fine grit, buffering agent, and water.
- Tumble for 1 to 2 days.
- Tumble calcite once more to shine with Aluminum Oxide polish and dry corn cob.
Buffering Agents
When using the dry tumbling technique for calcite, it is important to use a buffering agent during the fine grit stage.
A softer stone like calcite will yield better-tumbling results if there is a buffering agent to cushion the rocks as the volume of the stones decreases during tumbling. A buffering agent is instrumental in giving the mineral a nice shine.
Different types of buffering agents exist, such as ceramic media and plastic pellets. Ceramic pellets are popular, but they are better for harder stones. Plastic pellets work very well for softer stones like calcite.
Plastic pellets are:
- $2-$4 per pound
- Reusable and durable
- Easy to clean
I personally recommend using plastic pellets by Polly Plastics. They offer the best quality and are made in the USA. Check the latest prices on Amazon here (Amazon link).
Barrel Size
It is best to use a smaller barrel for softer stones. The bigger the barrel, the more room the stones have to move around and break apart. So, for tumbling calcite, be sure to use a barrel that is on the smaller side.
Throughout the process, you want to minimize the amount of erosion and breakage. Keeping the barrel size small will ensure that you get the biggest pieces of calcite possible.
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)
In Conclusion
Sure, it is possible to tumble calcite, but it will take a lot of time and effort to get it right. Because it is such a soft stone, you must take extra precautions to ensure the rocks don’t disintegrate into pebbles.
Remember to tumble calcite dry, use a buffering agent, and don’t keep it in the tumbler too long. Do some research about the best equipment to use, and you’re sure to have some beautifully polished calcite in no time!
TIP: Do you know that you can find fake calcites for sale on the internet? Find out how to spot fake calcite in the article below:
Real vs. Fake Calcite: Focus on These 6 Differences