Tumbling Your Crater Rocks


Greetings from Crater of Diamonds State Park! Many park visitors like to clean and display their Crater rocks and minerals at home. One of the most popular ways to clean and polish stones is through the hobby of tumble polishing.

Tumble polishing requires a rock tumbler, a machine that uses repeated impact and friction to smooth and polish rocks and minerals. There are different sizes of rock tumblers, but most have a watertight barrel rotated by a motor throughout the tumbling process.

Almost any rock that is hard, dense, and smooth can be tumbled. When visitors have their rocks and minerals identified at the park, we often tell them which stones are great for tumble polishing and which are not. Some of the best candidates from the Crater include quartz, agate, amethyst, and jasper. The rocks that you tumble should be free of cavities and fractures, with a smooth texture.

In tumble polishing, hardness determines how long you may need to tumble a type of rock or mineral. Stones of similar hardness should be tumbled together. Use the Mohs Hardness Scale to determine the hardness of minerals relative to other objects. For example, calcite, which is softer than a penny, erodes quickly in a rock tumbler and may not be suitable for beginning tumble polishing. Jasper and quartz, which are harder than steel, must be tumbled for several weeks to polish successfully. A good rule of thumb is to start out tumbling rocks and minerals that are harder than steel. Use a fingernail file or pocketknife to test stones before tumbling. Another helpful tip is to look for stones that have unique patterns or colors. Tumble polishing can bring out the hidden beauty of these stones even more.

The tumbling process can be divided into at least four stages, including three grinding steps and a final polishing step. Start by placing the rocks, water, and an abrasive grit into the barrel according to your rock tumbler instructions and tumble for 24 hours a day. The grit is usually man-made silicon carbide, which comes in at least three sizes.

Check the stones every few days to monitor their progress and prevent heat buildup in the tumbler. Once the rocks have tumbled for about a week, clean them thoroughly along with the barrel. A popular method is to use a colander to wash the rocks several times. Always clean your rocks outside; never wash tumbling grit into plumbing, as it sets up like concrete and will block your pipes.

Patience is key! Carefully check your stones after cleaning. If you notice they are still rough, tumble them again with new grit of the same size before moving to a finer grit.

Once your stones are perfectly smooth, it’s time to polish them. There are different types of polishing compounds you can use. The most common is aluminum oxide. Add polishing compound and water to the barrel with your stones and tumble for about a week. If your rocks look hazy after polishing, a trick is to use a bar of unscented Ivory soap. Grate the Ivory soap into the barrel with your rocks and water, and tumble for about 30 minutes to reveal that glossy finish.

Whether you enjoy rock tumbling or not, many beautiful rocks and minerals in addition to diamonds can be found at Crater of Diamond State Park! For more information, visit www.CraterofDiamondsStatePark.com, call 870-285-3113, or email CraterofDiamonds@arkansas.com.

Search area last plowed: September 27, 2022

Most recent significant rainfall: December 14, 2022

Diamond Highlights (100 points = 1 carat):

December 7 – David Anderson, Murfreesboro, AR, 7 pt. yellow
December 8 – Jeffrey Peek, Lonoke, AR, 1.20-carat brown
December 11 – Nicholas Richter, Longmont, CO, 24 pt. white
December 12 – David Makkos, Sandusky, OH, 22 pt. white
December 14 – David Murray, Anderson, IN, 3 pt. yellow

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