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Rock tumbling can transform plain stones into gorgeous pieces that highlight each rock’s unique qualities. Like many hobbies, though, rock tumbling has intricacies that are important to understand so that you do not damage your rocks. It is important to know what kinds of rocks are okay to go to a tumbler.
Moonstone is a popular type of stone to use for décor and jewelry pieces, and you can tumble it with other rocks of the same hardness. While you can tumble a piece of moonstone exclusively with other moonstones, you can also use rocks that have the same hardness. Stones like amazonite, labradorite, and opal are suitable to be tumbled with moonstone.
Rock tumbling is an easy way to turn dull, rough rocks into shiny beauties that have distinct qualities. Even with a rock that may not be a rare type, you still want to be careful when you start rock tumbling to prevent damage to the stones. Not all rocks can be tumbled with each other, and moonstone is no exception.
If you are interested in checking out beautiful tumbled moonstones you can find them by clicking here (Amazon link).
The Basics of Tumbling Moonstone
As you start rock tumbling, you will quickly realize that distinguishing the types of rocks you have is not only important for correctly identifying their type, but also for treating them properly.
Even though we may think of rocks as extremely hard, they have varying degrees of hardness that are key to know.
What is Moonstone?
Moonstone is a type of stone from the feldspar group that is primarily the mineral orthoclase. When moonstone is formed, its minerals fall into different layers, which creates the adularescence effect of light going across a gem.
You can find moonstone naturally in brown, grey, white, peach, green, or even colorless hues. Although it is part of the most common mineral group on Earth (feldspar), moonstone is quite different in appearance from other feldspar minerals, which makes it one of the most familiar types.
Moonstone ranks between a 6 and a 6.5 on the Mohs Hardness Scale, which is the standard system of measuring rock hardness. Feldspar stones fall in this category of hardness, which has many other types that make it easy to find rocks to tumble moonstone with.
Mohs Hardness Scale
The scale ranges from a 1, which can be scratched by something as soft as a fingernail, like talc or gypsum, to a 10, which takes more than a drill bit to damage, like a diamond.
The feldspar group that contains moonstone falls on the scale at a 6 to a 6.5, which places it harder than most other types of minerals. On the Mohs Hardness Scale, a stone that is at a 6.5 ranking relates to damage from a steel nail.
It is important to reference the Mohs Hardness Scale when you want to tumble rocks. If you put rocks of higher hardness, such as a topaz that ranks at an 8, with softer rock, such as a malachite that is only a 3.5 or 4, you will not have good results.
The harder rock will need to tumble for longer, which will be far too long for the softer rock. The softer rock will essentially crumble in the process. In contrast, when you put rocks of the same hardness in a tumbler, the rocks will need the same time to tumble.
BTW: Do you want to know more about rocks and minerals identification? The books listed below are the best ones you can find on the internet (Amazon links):
- The Crystal Bible
- Smithsonian Handbooks: Rocks & Minerals
- Gemstone & Crystal Properties (Quick Study Home)
- Ultimate Explorer Field Guide: Rocks and Minerals (National Geographic Kids)
What is Rock Tumbling?
Rock tumbling is a process that mimics the natural ways that rocks are changed by Earth. Rock tumbling imitates what the ocean does in the natural world; rocks are tossed against each other, sand, and water until they are smooth.
Typically, rock tumblers take between four and six weeks to result in polished rocks. Although this may seem like a long time, it is nothing compared to the length of time needed for rocks to become polished by nature.
For rock tumbling, you need a rock tumbler, water, silicon carbide grit, and rocks. You should have rocks with the same hardness but in a variety of sizes.
Small rocks help to smooth all the edges of larger rocks. The harshness of your grit will depend on the hardness of your rocks and the stage of tumbling you are at.
TIP: By the way, can you tumble rocks without a rock tumbler? Well, in some cases, you can. I wrote an article about this topic, check it out here:
How to Tumble Moonstone
Each rock tumbler will have its own instructions for specific details, but there are also general steps to polishing rocks that will apply to most rock tumblers.
Keep in mind that rock tumblers can be noisy, so consider placing yours in a garage or other space that is not going to be an issue.
As with any rock tumbling project, you should aim to use a mix of moonstone sizes. Some of the moonstone rocks that you include might only be around a quarter of an inch big, and others will be an inch or more. This helps the bigger rocks become smoother.
You should try to have rocks of a similar surface shape; try not to put sharp-edged rocks in with rounded-edged rocks because they will need different times to tumble.
The goal should be for the rocks to scratch each other the same amount, which ensures that they are the same hardness and similar surfaces.
Round the Surfaces of the Rocks
Typically, you will start tumbling moonstone with 80 to 120 silicon carbide grit, depending on how smooth the rocks already are.
Fill the barrel of your rock tumbler around ½ to ¾ of the way full of your rocks. Refer to your tumbler’s instructions for specific amounts of grit to add per barrel.
Add water to the barrel until it reaches just underneath the top layer of rocks. After you seal the barrel, start the rock tumbler. Check on it daily; you may have to open the tumbler to let the gas out if it starts to swell up.
This step should take between seven and ten days. The goal is to have all your rocks’ surfaces be rounded. Once this has been achieved, empty the barrel.
The old rock bits, grit, and water will form slurry during the tumbling process, and it will damage your plumbing if you pour it down the drain.
Clean the Rocks and Tumble Again
Carefully clean out the barrel of your rock tumbler and scrub your moonstone with a toothbrush to make sure there is no coarse grit left. Add the rocks back to your clean barrel and use 120-180 silicon carbide grit.
As you have already tumbled the moonstone through one cycle, the load will be smaller this time. You may need to add plastic pellets to get them to the same size load as before. Add grit and water as you did with the coarser grit.
Tumble the moonstone like this for another seven to ten days. The rocks should have a matte finish by the end of this stage. There should be no scratches left on the rocks’ surfaces at this point. Check on the load daily as you did in the previous stage.
Start to Pre-Polish the Rocks
Empty the barrel again and clean the rocks to remove all traces of grit. For this stage of tumbling, you will use 600 silicon carbide grit. You will likely need to add even more plastic pellets to get to a full load. Fill water to the same level.
Tumble the moonstone for another week. After one week, test one of the rocks to see if it is ready for polish. Use a piece of leather or damp feet to rub a small amount of polish onto the rock. If the stone does not get a good shine, tumble for another day. Continue trying the polish every day until the rocks are ready.
Finish Polishing the Rocks
Empty and clean the tumbler barrel. Clean your moonstone carefully. Try to get rid of all traces of grit. Instead of adding grit, this time, you will add a polish compound.
The amount you need will depend on your tumbler, so refer to the instructions for it again.
Using plenty of plastic pellets, add the stones back into the barrel. Add the correct amount of polish compound for your tumbler before filling water to the normal level. Tumble the rocks in the polish for five to seven days.
When your moonstones look the same dry as they do when they are wet, they are sufficiently polished. Be sure to clean them off and clean your rock tumbler when you are done.
TIP: Before you start tumbling your moonstones, you need to find them first. Check out the best rockhounding places in the US!