Rock Tumbler Blog

What is Crackle Quartz?

Crackle quartz is a crystalline quartz that has been intentionally fractured by people. They usually heat rock crystal or slightly translucent quartz to a high temperature, then suddenly quench it in cold water. The shock of sudden cooling causes a network of tiny fractures to propagate through the quartz.

If dye is added to the quenching water, it will enter any surface-reaching fractures and flow, by capillary action, deep into the quartz.

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Replacing Thumler's UV-10 Vibratory Tumbler Motor

We sell replacement motors for Thumler's UV-10 tumblers and decided we should give our customers a little guidance on how it is done. With just a few tools and a little bit of time you can replace a worn out motor on the UV-10 vibratory tumbler. The tools that you will need are 1) flat head screwdriver, 2) small crescent wrench, 3) vice grips and 4) clear silicone caulk.

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Thumler's Model B Tumbler Barrel and Liner Dimensions

Lots of people have written to us asking for the dimensions of the Thumler's Model B rock tumbler barrel and for the dimensions of the rubber liner and lid gasket.

Some people want this information to determine if the dimensions of this barrel are appropriate for the objects or materials that they want to tumble. Others want to know if the barrel or its liner can be used with a tumbler or barrel that they purchased a long time ago. We have prepared diagrams that clearly present the dimensions of the barrel and liner.

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Electricity Costs of a Rock Tumbler ?

Running a rock tumbler has an electricity cost. Depending on where you live and which tumbler you use the cost can range from negligible to shocking. Running a small tumbler in a state with low electricity costs can be as low as $1.16 per month. But if you run a large tumbler in a state like Hawaii where electricity rates are high the cost might be as much as $26.44 per month.

In this article we give you the information needed to estimate electricity costs for several different tumblers using the average cost of electricity for each of the fifty states.

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Jewelry Glue and Epoxy for Gemstones and Metal

If you visit a craft store to get glue for a jewelry craft project you will probably be surprised at the enormous number of glues that are offered for sale. We recently visited a Michaels craft store and found at least fifty different varieties of glue. Why so many varieties? Each one performs best on different materials or under different conditions - and competing manufacturers are trying to earn your purchase.

We purchased several glues that we thought would work well and brought them back for testing...

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Can I Use Sand in a Rock Tumbler Instead of Grit?

Some people write to us asking if they can use beach sand in a rock tumbler instead of grit. This sounds like a reasonable idea because sand is the abrasive material that is present when rocks are naturally tumbled in a stream or at a beach. However, you will probably be disappointed by its performance in a rock tumbler for three reasons...

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Polishing Igneous and Metamorphic Rocks

The house where we live is surrounded by shrubbery, small trees and other landscape features. A ground cover of rounded stream gravel was placed around most of these plantings by the previous owners.

I have a hard time walking past these rocks without seeing an interesting pebble that begs for examination. I believe that most of this gravel was dredged from the Ohio River where a few erratic igneous and metamorphic rocks are mixed with the local sedimentary rocks. These igneous and metamorphic rocks were carried south, from Canada, by glaciers and meltwater streams during the Great Ice Age...

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Polished Petoskey Stones

A Petoskey Stone is a fossil of a colonial coral (Hexagonaria percarinata) that lived in a shallow sea during Devonian time about 350 million years ago.

When the corals died they were covered with sediment and became part of a rock unit known as the Alpena Limestone. The Alpena Limestone outcrops along the coast of Little Traverse Bay near the city of Petoskey, Michigan - which is the town for which the stones have been named.

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Dyed Stones - Agate, Howlite, Magnesite, Quartz and More

Dyed gemstones are stones that have been treated with a dye to alter their color. The purpose of the color alteration is to increase their visual appeal or marketability. The stones selected for dye treatment are usually those that are nice gemstones in every way, but they simply have a color that is plain, weak or uninteresting.

Lapidaries (people who work with gem materials and ornamental stones) have used a wide variety of methods to change the color of stones for thousands of years...

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What is Dalmatian Stone? - It is not a Jasper

"Dalmatian Stone," also called "Dalmatian Jasper," is a white to cream-colored material with black spots that is produced in Chihuahua, Mexico. It reminds people of the Dalmatian breed of dogs - and that is where it gets its name. It is very easily polished to a bright luster and is a familiar semi-precious stone that is cut into beads, spheres, cabochons and carvings. It is also commonly seen as tumbled stones.

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Dyed Howlite and Magnesite - The Turquoise Impostors

If you have looked at inexpensive gemstone beads, cabochons, and tumbled stones, your eye has probably been drawn to a sky-blue material with a semi-gloss polish that looks exactly like turquoise. Many pieces even have the gray to black veining often seen in genuine turquoise specimens from the Bisbee and Sleeping Beauty mines.

This material probably isn't turquoise. Most likely it is another mineral, howlite or magnesite, that has been skillfully dyed to colors so similar to turquoise that it fools almost everyone. The gray to black veining aids in the deception...

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Phooey! My Stones Didn't Take a Nice Polish!

Tumbled stones with a fantastic polish do not happen by chance. They are produced by very careful and deliberate actions by the person who does the tumbling. Producing a great polish requires the five ingredients below. If any one of these is missing, a poor polish will probably be produced.

Quality rough materials
Proper rough preparation
Cleanliness in tumbling
Proper sizing and cushioning
Quality abrasives and media

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Sources of Colored Glass for Polishing

If you want to make some tumbled glass the first thing that you need to do is to find some rough glass. We are always on the look-out for interesting materials that we can tumble and in the article below we share a few of our sources with you.

We prefer to purchase glass that is already the desired size for tumbling. We also like glass that is blocky in shape, transparent, gemmy and colorful.

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Amazing Agate, Jasper, Chalcedony & Quartz Crystal

In this post we share photos of some amazing tumbled stones of agate, jasper, chalcedony and quartz that have caught our eye over the past several years.

Four of the many described specimens are pictured at right. They include a beautiful blue piece of tumbled lapis lazuli flecked with gold crystals of pyrite, four specimens of agate with wonderful eyes, a piece of green fancy jasper spattered with the markings of a bloodstone, and a piece of gray agate with banding that is so fine that it produces an optical effect when you look through it.

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Fee Mining and Digging for Gems, Minerals, Crystals

Fee mining sites are places where you can pay a fee to dig for rocks, minerals or gemstones and keep whatever you find.

There are many places in the United States where you can pan for gold and have a reasonable chance of finding some. There are also places where you can find ruby, sapphire, opal and many other gemstones. We have been to fee mining sites a few times, had some fun and found some nice materials.

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The Properties of Hematite

We sell over fifty varieties of tumbled stones and hematite is one of the most popular. People enjoy its mirror bright luster and its silver color. But, most of all, they are delighted by how its high density produces a "hefty" sensation when it is handled.

There are a number of products being sold with the name "hematite", such as "magnetic hematite" and "iridescent hematite". Most of these products are man-made. We will tell you what they are and how to spot them.

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Cleaning and Polishing Coins in a Rock Tumbler?

Quite a few people write to us and ask how they should clean and polish coins in a rock tumbler.

We are sorry but we do not give advice on this topic.

Why? We believe that coins should not be cleaned in a rock tumbler because the tumbling will cause severe damage to the coins. We also believe that it is impossible to put a genuine "polish" on coins with a rock tumbler.

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Comparing Thumler's and Lortone Small Rotary Tumblers

This is a feature-by feature review of the Lortone 3A rock tumbler and the Thumler's A-R1 rock tumbler. All of the information below is also relevant to the two-barrel tumblers made by these companies, the Lortone 33B and the Thumler's A-R2.

All four of these tumblers are high-quality machines that will last through years of regular use. They are much better than the inexpensive toy tumblers with plastic bases and plastic barrels that make an enormous amount of noise. We have sold hundreds of Lortone 3A / 33B and Thumler's A-R1 / A-R2 tumblers and have seen very few problems.

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Oiling A Thumler's Tumbler Motor and Bearings

Thumler's Tumblers should be oiled after each month of operation. The motor should be oiled and the bearings should be cleaned and oiled.

These are very easy jobs. Oiling the tumbler will prolong its useful life and help it run more quietly.

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Will You Polish This Rock ?

We occasionally hear from someone who has a special rock that they would like to have polished. The person does not own a tumbler, but has a one-time interest in improving the appearance of a special rock or a small number of rocks. Maybe they do own a tumbler but would rather have the job done by someone with more experience.

We don't offer this service because we would return most rocks to their owners without trying to polish them. Why? Because at a glance we would determine that the rock has a fracture or a shape or a texture or a mineral composition that will not work well in a rock tumbler.

Most rocks can not be polished in a rock tumbler.

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Polishing Marbles in a Rock Tumbler

Can I polish marbles in a rock tumbler?

Lots of people ask us this question. Our answer is "Yes, you can polish marbles." In this article we are going to describe a method that we have used to successfully polish a few marbles. There are many other methods that can be used. This is just one of them that works.

Should You Polish Marbles?

Some people use a rock tumbler to polish marbles that have light scratches and "hit" marks from being played with. Many people who collect valuable marbles will tell you that this should never be done. They would rather have a marble that shows signs of play - or even chips - than own a marble that has been polished.

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Fluorescent Opal - Virgin Valley Nevada

Some specimens of opal display a fluorescence under short-wave ultraviolet light. We recently tumbled some common opal from the Royal Peacock Mine, located in Virgin Valley, Nevada. It has a very strong green fluorescence.

To check the fluorescence of opal a short-wave ultraviolet lamp is needed. The "black lights" sold at novelty stores produce light of the wrong wavelength.

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Cleaning Your Rock Tumbler Barrel

A spotlessly clean rock tumbler barrel is the best way to achieve a great polish and prevent leaks. Two minutes spent on a thorough cleaning of the barrel can make a big difference in your tumbling results.

A clean barrel prevents particles of coarse grit from remaining in the barrel when you move to the medium grit step. A few particles of coarse grit in the barrel during the medium step will scratch up your rocks and ruin your polish.

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How Is Borax Used in Tumbling?

Some people use borax in their rock tumbling - the "20 Mule Team" type of borax - sold in the laundry section of your grocery store. They use it for burnishing. They also use it for a short, soapy clean-up tumble between grit steps.

We tested borax in the many roles that people talk about. We found it effective in some, and in some uses we did not see any difference between adding a little borax and not using any borax at all.

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Vintage Rock Tumbler Parts

Did you recently purchase a rock tumbler at a yard sale or an online auction site? Then, while cleaning it up, you discovered that the belt is brittle or the motor does not work?

Lots of these tumblers never get back into action. Why? They need an impossible-to-find part. These tumblers end up being resold and resold again because the buyer can't find the parts needed to get them running again.

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Are Tumbled Stones Valuable?

We really like tumbled stones and we would love to tell you that they are extremely valuable but most of the time that would not be true.

Most of the time, the price of tumbled stones is based more upon their "cost of production" instead of their "intrinsic value".

Most commercially tumbled stones are manufactured in batches of a few thousand pounds from common materials. The "cost of production" for these stones is typically...

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Swoboda Gem Trees - The First Tumbled Stone Trees

Swoboda Jewelry manufactured the first tumbled stone jewelry made in the United States. They also made wonderful gem trees in a variety of styles. The bonsai-style tree shown at right was made by Swoboda Jewelry.

The trunks and branches of these trees were made from a single base metal casting that was typically gold plated. The branches had pads where a number of colorful tumbled stones were glued to produce small flowers or a cluster of leaves. The tumbled stone flowers were made of gemstone petals surrounding a pearl or gemstone bead.

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Polishing Cabochons and Beads in a Rock Tumbler

If you cut cabochons, beads or other small lapidary items you might be able to save a lot of time by allowing a rock tumbler to do the final sanding and polishing steps. A tumbler will produce a uniform, super bright polish on almost any small, smooth object made from agate, jasper, quartz, petrified wood or other lapidary material with a Mohs hardness between about 5 and 7.

The Brazilian Agate cabochon at right was cut to shape using a rock saw and diamond wheel, then briefly sanded on an expanding drum to remove ridges left by the diamond wheel. It was then placed in a rock tumbler for final sanding and polishing. The result is a cabochon with a fantastic polish, smoothly cambered edges and a nicely polished back...

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Spectacular Eye Agates

An eye agate is an agate that exhibits one or more round concentric markings known as "eyes." The photo at right is a piece of carnelian agate from Botswana that has several beautiful eyes.

As a general statement, eye agates are rare. However, some localities are well-known for producing eye agates. Carnelian, gray, and pink agate nodules from Botswana, a small country in southern Africa, often contain eyes. Lake Superior agates found in the Great Lakes area of the United States frequently contain numerous colorful eyes...

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Polishing Precious and Common Opal

Precious opal and common opal can be shaped and polished in a rock tumbler. Be warned before you try it that this is a great way to waste a bunch of nice and often expensive opal if you don't know what you are doing or if you don't pay careful attention to what is happening in the barrel.

Here are a few important things to keep in mind before you load the barrel...

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What is Silicon Carbide Grit?

Silicon carbide is a compound composed of silicon and carbon with a chemical formula of SiC. It is one of the hardest known materials with a Mohs scale hardness of 9+. It is also inexpensive, selling for just a few dollars per pound as a screened and packaged product. The combination of hardness and low price make it an excellent abrasive for rock tumbling, lapidary work, sandpaper coating, sand blasting and water-jet cutting...

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Fluorite Tumbled Stones - Fluorescent!

Fluorite is one of our favorite minerals. We enjoy how it can have "color bands" that range from colorless through yellow, green, blue and purple. The various colors in fluorite are caused by impurities in the mineral. These banded specimens make beautiful tumbled stones.

If we take fluorite into a dark room we are unable to see it. However, if we have an ultraviolet light (which produces light that is invisible to humans) and shine it on the fluorite, the fluorite will probably glow a beautiful blue in the dark as long as the ultraviolet light is shining on it.

The pair of photographs at right show banded fluorite under normal light (top photo) and in the dark under ultraviolet light (bottom photo).

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Polishing Ohio Flint into Gemstones

One of the first rocks of value in the area that we now call "Ohio" was flint. As early as 12,000 years ago, the Native Americans of Ohio recognized flint as a hard, tough, durable rock that could be chipped or flaked into sharp tools and weapons. These people traveled long distances to collect the flint.

One locality was especially important. That was a ridge in eastern Ohio where the Vanport Flint is exposed in outcrop. The area is now known as "Flint Ridge." There, Native Americans dug hundreds of shallow quarries along the crest of the ridge to produce flint.

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Save Time and Money with a Vibratory Tumbler

Vibratory tumblers can produce tumbled stones in less than 50% the time required for a rotary tumbler. That enables you to process more stones per month and spend less money on electricity per pound of rock processed. In addition, vibratory tumblers only require about 25% as much grit and polish compared to a rotary tumbler. That will save you a lot of money.

Other important differences between vibratory and rotary tumblers are the action that occurs in the barrel and the shape of the stones produced. Rotary machines rely mainly on the tumbling action...

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Operating the Thumler's UV-10 Vibratory Rock Tumbler

In this video we demonstrate how to operate the Thumler's UV-10 vibratory rock tumbler. The key to success in operating this tumbler is adding just the right amount of water. You want just enough water to make the grit stick to the rock and lubricate the material for a vigorous tumbling action. If you add too much water the grit will wash off of the rock and drop to the bottom of the barrel.

After you have the tumbler running it is very important to check it at least two or three times per day...

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How Much Do Stones Weigh?

How many pounds of tumbled stones will you need to use them as ground cover in a potted plant or to fill a decorative jar?

It is very easy to estimate the amount of stone needed if you know the size of the jar and how much the stones weigh in pounds per cubic inch.

This works for small projects such as filling a planter, but it can also be used for estimating how many tons of stone will be needed in a landscaping project.

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Used Rock Tumblers

Lots of people think about purchasing a used rock tumbler to save money. A used machine can be an intelligent purchase if you get a fair price and know how to determine if the tumbler is in good running condition. If you are thinking about purchasing a used tumbler, here are a few things to consider...

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Smithsonian / Rolling Stones Rock Tumbler

This little plastic rock tumbler has been around for a long time. Sold since the 1970s in a number of models under a variety of different names, the "Rolling Stones Rock Tumbler" is probably the best-selling rock tumbler of all time. Its popularity comes from its low price and from its presence in the stores of several major retail chains.

The tumblers are always sold as part of a kit that contains everything needed to tumble a single batch of rocks. The kit typically includes: tumbler, barrel, rough rocks, silicon carbide grit, rock polish and instructions...

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Vintage Swoboda Jewelry

The popularity of tumbled stones in the United States was kindled by a jewelry project launched by Edward Swoboda of Los Angeles in the early 1950s. Mr. Swoboda was a mineral dealer who received a shipment of tourmaline and beryl that was of lower quality than he had hoped for. He decided to craft some of the colorful specimens into smooth baroque shapes, polish them by hand and mount them in jewelry.

His experiment was an enormous success. People wanted more jewelry than he was easily able to make by hand. What a great problem to have! He knew that he needed a way to mass-produce baroque-shape stones with a high polish...

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Ocean Jasper Glows Under the Black Light!

We have an ultraviolet lamp that we use for viewing fluorescent minerals. One day we decided to use it to view some tumbled stones. We were really surprised when we viewed Ocean Jasper. Many of the orbs and some of the swirls had a delightful fluorescence - under both short wave and long wave ultraviolet light!

Not all specimens of ocean jasper glow in ultraviolet light; however, we have viewed a lot of specimens and most of them fluoresce to some degree under both short wave and long wave ultraviolet light.

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Books About Rock Tumbling

Quite a few books have been written about rock tumbling since the hobby became popular in the United States during the 1950s. Most of these books have gone out of print and copies are really hard to find.

The best book that is currently in print (and the best book of all time, in our opinion) is Steve Hart's Modern Rock Tumbling. It covers just about every aspect of rock tumbling, from collecting and preparing your rough to polishing and burnishing.

Here is a list of all of the rock tumbling books in our library...

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Where is the Best Place to Run a Rock Tumbler?

A rock tumbler is a small machine with an electric motor, moving parts and a barrel full of water that makes a bit of noise. Those are the things that you need to consider when picking a location to run it. Actually, it is sometimes easier to decide where you don't want to run a tumbler. Let's consider these items one at a time to rule out a few places at your house.

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Compare Vibratory Rock Tumblers

Lots of people write to us asking if they should purchase the Thumler's UV-10 Vibratory Rock Tumbler or the Lot-o-Tumbler Single or Twin. The answer to that question depends upon a few things:

What are you going to tumble?
Where will you run the tumbler?
How much rock will you be processing?
Are you willing to glue a tumbler to a block?

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Fluorescent Moonstone - Tumbled Stones

We tested some moonstone with our ultraviolet lamp and were really surprised at the beautiful red fluorescence.

The gemstone known as "moonstone" is an alkali feldspar mineral known as anorthoclase or adularia. Some specimens exhibit a beautiful red fluorescence under short wave ultraviolet light as shown in photographs at right.

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Skilcraft Rock Tumblers

Skilcraft Rock Tumblers were widely sold in the United States during the 1970s. The model shown here was available in 1972. Their marketing slogan was "Convert rough rock into sparkling gemstones!"

This Skilcraft tumbler had a very small octagon-shaped barrel that processed about 1/2 pound of rock. The barrel was made of plastic with a metal screw-on lid. To reduce the amount of noise produced, the metal lid had a foam rubber liner glued to the inside surface. The kit came with a rectangular piece of rubber to line the inside of the barrel...

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Zebra Jasper - Brown and White Stripes!

We recently tumbled some nice brown and white zebra jasper. They call it zebra jasper because of the stripes. (Yes, we know that most zebras have black stripes. However, young zebras do have brown stripes during their first year. You can confirm that here.)

In this article we will share how we tumbled this material...

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Who Buys Rock Tumblers?

We have been selling tumblers for years, and we see lots of rock tumblers going to Alaska, the Northwest, New England, the Great Lakes Region and the Southwest. The residents of states in these regions purchase more rock tumblers per capita than the national average.

We have some ideas why tumblers are so popular with the people who live in these areas...

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Rapco "Tumble Stones" Rock Tumbler

The Rapco "Tumble Stones" rock tumbler was sold in the early 1970s. It was one of the first inexpensive plastic rock tumblers on the market and had a suggested retail price of $17.95 in 1972. It was marketed as "A lapidary set for family use."

We enjoy their product slogan... "Transform rough rock into Precious Gems."

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Paint Can Rock Tumbler: Thumler's Model A

The first small-scale rock tumblers for hobbyist use were manufactured in the 1950s. Many of these early machines used metal paint cans as barrels. Paint cans worked, but they were less than the ideal barrel for a number of reasons which included: 1) the metal barrels made the machines incredibly noisy; 2) the paint can lids often popped off when gas pressure built up in the tumbler barrel; and, 3) the grit and rocks tumbling in the barrel quickly abraded holes in the thin metal barrels.

The photos at right are a Thumler's "Model A" double-barrel rock tumbler manufactured in the late 1950s and...

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Gas In the Rock Tumbler Barrel?

Some materials will produce gas when you run them in a rock tumbler. Man-made glass and natural glasses, such as obsidian and Apache tears are known gas producers. Other types of rocks can also produce gas.

A gas build-up in the tumbler barrel can pop off the lid and produce a big mess. This article explains a few ways to avoid that problem.

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Beautiful River Stones

"River Stone" is a product that always catches my eye at landscaping and garden centers. These river-tumbled stones can be beautiful when they come from a river that flows over a variety of interesting and colorful rock types. We have a nice cover of river stones around the shrubbery that borders our home. It contains a variety of igneous and metamorphic pebbles such as granite, schist, gneiss and gabbro. They look great and are especially attractive after a rain when the water enhances their color.

Occasionally I have seen river stone for sale that has a polished appearance like the stones in the photo at right.

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Rock, Gem and Mineral Shops in the United States

Click a state to see a list of rock shops in that state. What is a Rock Shop? A rock shop is a place you can visit to see some of the coolest rocks on our planet and buy some to take home. A good rock shop will sell rocks, minerals, gems and fossils of various kinds; books about rocks; and, beautiful things made out of rocks. A good rock shop is staffed by enthusiastic people who know a lot about rocks and can answer questions about them.

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Rock, Mineral, Gem, and Fossil Clubs in the United States

Joining a rock club is a great way to meet other people in your area with similar interests. You can also learn new skills, since some clubs offer classes in things like cabochon cutting, faceting, wire wrapping, and more, and they have a workshop with equipment available to members. Field trips to rock and mineral collection sites are another benefit of being a club member. Many clubs have monthly meetings which are open to the public, so you can stop by and check out a meeting without cost or obligation.

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Types of Rock Tumblers

Rock tumblers are made in many sizes and qualities, from toys to commercial grades.

Some are designed with the objective of being sold for a very low price. These tumblers might last through a few batches of rocks, but are not designed for long-term use. Some are high-quality machines that can last through decades of regular use, if carefully cared for and gently operated.

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Rock Tumbler Manufacturers and Brands

If you buy a rock tumbler and have problems after the purchase, where can you go for help?

We have put together a list of rock tumbler manufacturers and brand owners who we believe are in business today.

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RockTumbler.com Authors

Hobart M. King has decades of rock tumbling experience and writes most of the articles on RockTumbler.com. He has a PhD in geology and is a GIA graduate gemologist. He also writes the articles about rocks, minerals and gems on Geology.com.