Back into tumbling (rocks)

 kw: hobbies, rockhounding, lapidary, rock tumbling, jasper

In March 2008 my brother and I went into the upper Mojave desert, to Lavic, to collect jasper. I wrote about the experience at the time; this post includes several pictures of the jasper. This is a view from the collecting area on Lavic Lake, north toward mountains above the Sidewinder Dunes, a hiking area. The colorful mountains are part of the same series of ranges that includes Calico, which is to the northwest, closer to Barstow.

Looking down near my feet from the same spot, small chunks of the unique jasper known as Lavic Jasper are scattered everywhere. Rock collectors call this "float". More than a dozen pieces of red and brown jasper are seen in this picture.

My wife and I had collected here a few years earlier, but brought back only about ten pounds of rocks. This time my brother and I gathered closer to 30 pounds. 

After I got home I bought a small rock tumbler—on this trip I had visited the Diamond Pacific store in Barstow and obtained grinding grits and polishing compound—and began to tumble in earnest. 

I wore out the cheap tumbler I had bought, so I did more research to get a better quality one. I bought a Thumler's Tumbler, and it has the staying power I need. I finished the last batch of really "clean" stones, those with no serious cracks or pits, in 2012, and reported on the that batch then (with more pictures of the lovely material). I replaced the drive belt once during those four years of on-and-off tumbling.

A couple of months ago I decided to go through the remaining rough material and pick out some that might be worth tumbling. I eventually settled on about six pounds of chunks and pieces, weighing between 10 and 120 grams each. It's best to tumble a range of sizes together. The small rocks get into indentations in the larger ones and help them get abraded more uniformly.

I put just over two pounds (967 grams) into the tumbler along with an appropriate amount of rough grit and water, and set it going. After six days the drive belt broke. I ordered a replacement along with some extra parts I thought I should have as spares, such as the lid, which can wear through. Here is a picture of the larger stones after six days of tumbling. At the start they all had sharp corners.

The third one from the left in the top row features in what comes next. I like it because of its mix of red and green sections. Green is the rarest color for jasper. This picture is one of a series taken November 30, 2023.

I had weighed the stones before I started (967 grams), and I weighed them at this point (925g). The 42 gram difference is 4.3%.

I reloaded the tumbler, including a charge of fresh grit. These clearly need a lot more material removed. I let it go two weeks and then took the stone out, to inspect and weigh (842g, down another 8.6%). I took another series of photos. The yellowish stone at upper left had such a hole in the end that I decided to break part of it off. I added the 2g piece so removed when I reloaded the tumbler and ran everything another two weeks. More photos and more weighing (742g, down a further 10.3%, for a total removal of 23.3%).

I'll quickly show three examples of tumbling progress. Firstly, the green-plus-red one I pointed out above.

I did my best to take all photos at the same scale. Here we see some interesting things happening. Firstly, of course, the stone is getting smaller. The white mineralized crack is still there, and at the right, white mineralization has begun to appear at the tip of the stone. The deep crack at the opposite end shows that this stone may not be suitable for further rough tumbling. I may need to use epoxy filler. Finally, the green material is seen to be rather thin, and much of it has been abraded away. This is a further indication that I should fill the cracks and proceed to finer grinding and polishing with this stone.

Secondly, one of the red stones.

This stone began substantially smaller than the prior one, weighing less than half as much. In the left and middle views, there is a deep gouge, which is almost totally gone in the third view. I'll probably remand this to another round of rough grinding to see if some of the whitish areas can be removed.

Thirdly, a greenish yellow stone with red striping, quite a small one. It started out as about ten grams.

The smallest stones lose the most proportional mass. This one has lost nearly all of the big gouge, so it is almost ready for finer grinding.

This batch of stones is presently set aside while I rough grind another batch. I noticed that the two sessions of two weeks' duration resulted in a slurry containing no trace of the coarse grit I started with. The six-day run still had plenty remaining (which I added back in). For the batch that is running now, I'll start with a ten-day run, and adjust run times to just barely use all the grit.

It will be several weeks before I have more to report. My plan is to do rough grinding on all six pounds of stones, then select which ones to continue with for finer grinding and polishing, or mix-and-match them into two batches for finishing.