Rock Tumbling

After my son showed an enduring interest in rocks and minerals, I purchased the National Geographic Professional Rock Tumbler. It comes with the reusable tumbler, a pound of rocks, a color informational booklet, the grit used in tumbling, a strainer, and a few jewelry accessories. I find it is the perfect centerpiece for a unit study on the rock cycle and can pair well with earth science, chemistry (intro to the elements), and geography. Whatever direction you and your kid want to take it.

What I love about rock tumbling with a 5-year-old is how it teaches patience. The process takes a few weeks to complete, but you get to check on your rocks every few days to see how they have changed. If your child is ready to keep a research notebook, this would be an opportunity to practice simple observation and record keeping.

Here's what the rocks looked like on arrival:

The tumbler came with 1 lb of rocks. This is what they looked like before tumbling.

To polish these rocks, there are four packets of grit that you use in series, starting with the coarsest. The tumbler consists of a motor with belts and a watertight barrel. Getting started takes only a few minutes and my son was able to do most of it himself. Just open the barrel, place the rocks inside with Grit 1, then pour enough water to cover them. Seal up the tumbler, place it on the motor, press start...and be patient. The first step takes 3-5 days at high speed.

This is what our rocks looked like after four days being tumbled with Grit 1:

These are the same rocks after about 4 days of tumbling. Smooth, but not shiny.

My kids were impressed and liked comparing the before photo to the smooth rocks in front of them! They looked shiny when wet and dull as they dried off.

The messy part of this project is switching between grits. You can do this outdoors or set up a waterproof table covering. When you open the tumbler, you are left with the rocks in a slurry of rock powder, grit, and water (which cannot go down your house's plumbing). We went outside and poured the contents of the tumbler through the strainer into a disposable plastic tray (thanks, IHOP takeout!). We rinsed the rocks to see if they had rough edges and decided they were smooth enough to move on to Grit 2. Then we poured the slurry off outside and set up the next round of tumbling.

I find it is hard to mess this project up. If the rocks hadn't been smooth enough, we could have poured the slurry back in the tumbler. If you run it too long, the rocks are just smaller than the could have been. The time it takes to wear away the rough spots varies depending on the hardness of the rocks you start with. If you have your own rocks, you'll want to tumble batches of rocks with similar hardness. Time to pull out Mohs scale! (We are already collecting rocks to use in a second batch. I am excited to see what happens to our local finds when polished!) 

I will post updates after we are finished with Grits 2, 3, and 4. If you are thinking about buying this kit, here are a couple more things you should know:

After the first batch, you'll have to get more grit and a source of rocks if you want to do more. (There are many options online for rough rocks if you aren't planning to collect your own. Grit can be purchased on Amazon, and I'm still looking into other options.) This kit comes with only enough grit for one batch. The tumbler itself is reusable and is reputed to last years.

It is a bit noisy. I find it is not quite as loud as my dishwasher. In fact, it would make a great alternative to a white noise machine! We were slow to start using it because the kids didn't like hearing the sound at night, so we ended up putting it in the garage.

I picked mine up on sale, but there is also a cheaper version by the same company. I have not tried it out, however.

Got questions? Let me know in the comments!

(The links in this post are affiliate links. It does not change the price of the items, but if you purchase something I will receive a small commission.)