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 Home » Tumbler Rough » Montana Agate Rough

Montana Agate - Rock Tumbler Rough

Montana aagate tumbling rough

Montana Agate

Montana Agate is a clear to white to amber agate sometimes flecked with black and brown mossy inclusions.

The moss patterns are most interesting when the amount of moss is just a few percent of the material. Montana Agate is popular with people who run rock tumblers because it polishes easily to a very bright luster and yields beautiful agate and sometimes mossy surprises.

This rough consists of material that has been crushed to approximately 3/8" (9 mm) to 1 1/2"" (38 mm) diameter pieces - a size that will work well in your rock tumbler. It might also include a few small nodules, small slabs, and trim saw end-cuts. These can produce some nice tumbled stones.

We recommend TXP polish - an aluminum oxide compound - for polishing Montana Agate.

Photographed wet to show full color.

Polished Montana  Agate
We tumbled a four-pound batch of Montana Agate. The photo above shows a few nice pieces that we really liked. You can see that it is a transparent to root-beer colored agate with dots, streaks and dendrites of black and brown moss which would be called Montana Moss Agate. It polishes easily to a very bright luster. Our polishing procedure is described below:

Step 1: We started with four pounds of Montana Agate rough and placed it in a Lortone QT6 tumbler with eight ounces of coarse 60/90 grit and water. We ran the tumbler for about ten days and rinsed the rough. The pieces showed some nice rounding but we like really round tumbled stones. So, we loaded it back into the barrel for another ten days with coarse grit and a few large ceramic pellets to make-up for the volume lost in the first tumble. At the end of the second run in coarse grit the pieces were nicely rounded.

Step 2: We loaded the Montana Agate into a single barrel Lot-O-Tumbler and added enough large ceramic pellets to bring it up to recommended barrel capacity. We then ran it for three days in 150/220 grit, rinsing and adding new grit after 24 hours and again at 48 hours. At the end of three days we cleaned the rough.

Step 3: We then loaded the agate into the Lot-O-Tumbler barrel and added large ceramic cylinders to bring the barrel up to full capacity. We than ran it for 48 hours in the Lot-O-Tumbler with 500F grit prepolish. At the end of 48 hours the agate was starting to show a slight glossy luster so we cleaned it up and prepared it for polishing.

Step 4: The final step was 48 hours in the Lot-O-Tumbler with one tablespoon of TXP aluminum oxide polish. We checked the moss agate at the end of 24 hours and they had a really bright polish. We were tempted to stop there because the polish was so bright but we added 1/2 Lot-O cap of water ran it an extra 24 hours. The final polish was slighly improved. It was amazing how nice the polish was at the end of 24 hours.

We were really pleased with the polish and really liked the transparent stones with lightly distributed moss. Total processing time was twenty days in coarse grit and 7 days in the Lot-O-Tumbler.

Here is what the United States Geological Survey has to say about Montana Moss Agate:

"Montana moss Agate is the grayish-white to gray translucent chalcedony containing dendrites. The black, brown, or red tree-like or scenic dendritic growths are actually included minerals of manganese and iron. Most of the moss agate is found as water worn cobbles in the Yellowstone River or its drainages between Billings and Sidney. The material can be collected in Yellowstone, Treasure, Rosebud, Custer, Prairie, Dawson, and Richland Counties. The agate has long been a favorite of hobbyist and professional cutters because of the beautiful and highly variable patterns, the durability, and ease in cutting and polishing."

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