What is Tumbling Rough?
"Tumbling rough" is the name used for rock material that is used to produced tumbled stones in a rock tumbler. Agate, jasper, petrified wood and varieties of quartz are the most popular types of tumbling rough. Many other materials will produce nice tumbled stones.
To produce nice tumbled stones a person must be selective in the types of rock placed in a tumbler. Rock tumblers are not magical machines that convert ordinary rocks into beautiful gems. To produce beautiful tumbled stones, one must begin with beautiful tumbling rough. Also, that rough must have physical characteristics that allow it to be shaped and polished in a tumbler. Most rocks do not have these characteristics and will not produce nice tumbled stones. To achieve good results, you must select your tumbling rough with knowledge and care.
Characteristics of Good Tumbling Rough
The types of rocks that perform best in a rock tumbler are hard, tough rocks with a smooth texture.
"Hard" means that they are not easily scratched. Rocks that work best in a rock tumbler have a Moh's Hardness of between 6 and 8. People who are using a rock tumbler for the first few times will have best results using rocks in this hardness range. Some softer rocks can be shaped and polished in a tumbler, but special materials, knowledge and skill are required.
"Tough" means that they are not easily broken. Rocks that chip easily or materials that have cleavage can sometimes be shaped and polished in a rock tumbler. Again, special materials, knowledge and skill are required.
"Smooth texture" means that the rocks are not granular, porous or internally fractured. Granular rocks will shed grains during the tumbling process and these grains will scratch the surfaces of the rocks during the polishing step. Porous rocks will hold grit and rock particles in their crevaces and release them during the polishing step. Just like with granular rocks these fugitive particles will scratch the rocks in your barrel during the polishing step. Fractured rocks perform poorly because they break forming sharp edges that will scratch the other rocks in the barrel.
In the paragraphs above you might note that rocks lacking hardness and toughness can often be polished using special materials, knowledge and skill. However, granular rocks, porous rocks and highly fracture rocks cause problems that special materials, skill and knowledge are unable to overcome. Most of the time these problem rocks are not suitable for tumbling and should be discarded or used for another purpose.
Agate, jasper, and quartz are hard tough rocks. But, before tumbling they must be inspected to remove pieces with pores and fractures. Tumbling poor quality materials is a waste of time, grit, polish, electricity and wear on your tumbler.
It is better to spend a few minutes inspecting your rough before placing it in a tumbler than opening the barrel after a month of waiting and work to find disappointing results. It is also better to spend a few more dollars on nice rough than it is to waste time and money tumbling junk. If you put junk in you will get junk out.
Agate, Jasper and Petrified Wood - Favorites for Rock Tumbling
Agate and jasper are two materials favored above all others for rock tumbling. They are favored because they often have beautiful colors and patterns. Agates are translucent materials that usually exhibit bands, plumes or mossy inclusions. Jaspers are opaque materials with interesting patters produced by inclusions of colorful mineral matter. More agates and jaspers are processed in rock tumblers than all other materials combined.
Petrified wood, also known as silicified wood, is a variety of jasper. It is a very popular tumbling rough and is found in many parts of the United States. It is colorful, often has interesting wood patterns and produces beautiful tumbled stones.
Agate and jasper usually shape nicely in a rock tumbler and polish to a bright luster. If you use these rocks in your tumbler and elimiate low quality pieces, you should be rewarded with nice tumbled stones.
Many people live in areas where colorful agate and jasper can be collected in streams, dry washes and walking the land atop ancient lava flows. Other people live where these materials do not occur. Fortunately, many rock shops and specialty websites sell rocks crushed and sized for rock tumbling. Nice jasper and agate can sell for as little as $5 to $10 per pound. Material with premium color and pattern can cost a little to a lot more. The price depends upon color, pattern and the material's popularity.
Varieties of Quartz
The mineral quartz occurs in all colors of the spectrum. A few of these varieties are long-time favorites for rock tumbling. These include: rose quartz (pink), smoky quartz (brown), amethyst (purple), lemon quartz (yellow), peach quartz (orange) and crystal quartz (clear). The colors are caused by trace amounts of impurities or defects within the crystal structure of the quartz.
Quartz is hard, tough, and usually has a smooth texture. However, it often requires a little more care during tumbling than agate and jasper. The care required is to make sure that the pieces are not tumbled roughly. If there is too much action in the barrel, pieces of quartz can be chipped, bruised or fractured.
This damage can be avoided by filling the tumbler to the proper level and adding small ceramic media, plastic pellets, or small pieces of rough to reduce the severity of impacts in the barrel. (We have an article about tumbling media that explains tumbling media in great detail.)
Aventurine Quartz and Tigerís Eye
Some specimens of quartz contain inclusions. Aventurine is a good example. It contains tiny particles of mica. Light entering the stone strikes the mica particles and reflects from them. This gives aventurine a sparkling luster. Aventurine has the characteristics of a good tumbling rough and produces nice tumbled stones. Aventurine usually costs about the same as nice agate and jasper but you can spend a lot more on premium materials.
Tiger's eye forms when the mineral crocidolite is replaced by quartz. Crocidolite is a fibrous material and the parallel quartz replacements reflect light. Round polished pieces of tiger's reflect light like a chatoyant "eye". Many people think these eyes resemble the eyes of a cat. That is how tiger's eye received its name.
The varieties of quartz mentioned above are often seen for sale as tumbling rough. They are usually inexpensive, costing between $10 and $15 per pound for prepared rough. Rough of premium color and condition sells for significantly more.
Tumbling Rough from Your Lawn and Garden Supply
Your local lawn and garden supply and the outdoor department at Walmart, Lowes, and Home Depot sometimes sell rocks that can be polished in a rock tumbler. We have purchased crushed granite, basalt cobbles, and quartzite "river stone" and polished them in a tumbler. If you like to tumble these materials the rough can cost less than $1 per pound.
Size of Tumbling Rough
Pieces of rough used for tumbling usually range in size between 1/4 inch and 3 inches in size. Small tumblers with a two or three pound capacity barrel work best when tumbling rough up to about 1 1/2 inch in size. Tumblers with a six to twelve pound capacity barrel can tumble rocks that are up to about 2 1/2 inches in size. Only two or three large rocks should be added to a load.
Some people collect or purchase large pieces of rough that weigh several pounds each. These large pieces of hard, tough rock are difficult and dangerous to break. We don't recommend that activity, even to people who have lots of rock-breaking experience.
We recommend collecting or purchasing rocks that are properly sized for your tumbler. Lots of rock shops and websites sell rock that is specially sized for tumbling. Nice tumbling rough is also offered for sale at many gem and mineral shows.
If you have large pieces of rough the best way to reduce their size is to take them to a rock shop with a rock crusher or a rock trimmer. Some rock shops will crush a few pounds of rocks for a fee of a few dollars. You will get back a bucket that contains your crushed rock. You can then take it home, wash it, inspect the pieces, and discard those that are poor candidates for tumbling. Some waste and undersized rock should be expected.
Before You Collect Tumbling Rough
Many people who run rock tumblers enjoy collecting their own rough. Collecting tumbling rough can be a great activity for family and friends. But, before you go out collecting, you need to know a few things about property ownership and mineral rights.
In the United States, all land, rocks and minerals are owned by a person, a company, an organization, or the government. So, before you enter any property, dig, or remove anything, be sure that you have explicit permission for what you plan to do, what you plan to remove, and what you plan to do with anything that you remove. If you do these things without permission you could get in trouble or even be arrested for tresspassing, vandalism or theft. Getting permission might be inconvenient or difficult but it is a lot easier than getting out of trouble.
Rock and Mineral Clubs
There are many rock clubs located in all parts of the United States. These clubs often have organized collecting trips. Being a member of one of these clubs is a great way to learn and a great way to obtain access to excellent collecting areas. The clubs often have swap meets where you can bring materials that you collected and trade them for different materials that another member collected. Rock clubs are great places to make friends, learn about rocks and obtain interesting rocks to tumble.
Fee Mining Sites
Fee mining sites are places that you can visit, pay a fee, look for rocks and minerals, and keep what you find. They are fun places to visit and, if you know what you are doing, you might find some really nice rocks. Skill and luck are both important parts of finding nice rocks. So, while you are there, pay attention the methods of successful people. They are often willing to provide advice that will improve your collecting skills. There might be a fee mining site near you. Find them here.
Breaking Tumbling Rough
We left this topic for last because we don't recommend it, but if you insist on breaking your own tumbling rough here are a few suggestions.
Breaking rock for your tumbler is hard, dangerous work. We highly recommend buying specially prepared tumbling rough from a rock shop or online rock dealer. That small expense will save you lots of time and you will have very little waste. It is great to tumble rocks that you have found yourself but if you can afford them, prepared tumbling materials are easiest to use. Another good alternative is to visit a local rock shop that has a rock crusher. For a small fee some rock shops will process a few pounds of rock for you.
Stay Safe! When breaking rock for use in your tumbler your number one goal is to protect yourself from flying rock fragments. Wear safety goggles to protect your eyes! Wearing gloves, heavy pants and a long-sleve shirt made from a heavy fabric is also highly recommended. Sharp rock fragments will fly when you hit a rock with a hammer. Heavy clothes and safety goggles are important protection. Finally, a dust mask should be worn to avoid breathing rock dust.
Impact-resistant safety glasses and gloves must be used when breaking tumbling rough!
Don't Damage Surfaces! Do not break rocks on a sidewalk, concrete porch, wooden deck or other nice surface. You will damage that surface. Good substrates for breaking rocks include: large durable rocks, large pieces of metal such as thick piece of steel or a small segment of railroad rail, or a large durable brick.
Don't Smash the Rocks! Another practice to avoid is simply placing the rock that you want to break on a hard surface and bashing it with a hammer. That might break the rock, but it will also induce a lot of internal fractures in the pieces that you produce. Instead place a small round piece of metal (such as a piece of concrete reinforcing rod) under the rock that you want to break. Finally, instead of bashing the rock with a hammer, use a hammer and a rock chisel.
To do this, place your round rod on your large rock or heavy piece of metal. Then rest the rock that you want to break on top of the rod. Now, strategically place a heavy chisel on the rock and tap it with your hammer. This causes the force of your hammer blow to enter the
rock at a single point and that force will transfer through the rock to the point where it is in contact with the metal rod. This enables you to break the rock with less force, produce fewer small pieces and cause less fracturing within the pieces produced.
Break the rock with small, well-positioned blows. You don't have to BASH it!
Contain Flying Debris: When you break rocks with a hammer and chisel some pieces are going to fly. To contain them, place your anvil in a heavy cardboard box that is at least on foot taller than the top of your anvil. Then when you break a rock the broken pieces will drop to the floor of the box and flying pieces will bounce off the walls of the box and be contained.
|This is a couple pounds of tumbling rough. Materials included are tigereye, brown agate, amethyst, green aventurine, rose quartz and blue quartz. .
|A nice piece of petrified wood suitable for rock tumbling. Note how it has a nice, smooth, non-granular texture. The pore spaces of the original wood were completely silicified and the piece is relatively free of fractures. It also has beautiful varigated color. Petrified wood like this is a wonderful find and would produce a beautiful tumbled stone. This piece is about two inches across.
|A few agate nodules from the Black River area of Argentina. These are large nodules of premium quality that will produce fantastic tumbled stones. They are about two to three inches across in size and cost a few dolllars each.
|Several colorful pieces of a japser known as "yellow feather" because of its elongate feather-like markings. It tumbles to a bright luster and produces attractive tumbled stones. These pieces are about two inches across.|
|Rose quartz and amethyst quartz are both forms of crystalline quartz that are popular for rock tumbling. They require cushioning with ceramic media or smaller pieces of rough to prevent chipping. The pieces shown here are about 3/4 to 1 1/2 inch across. This type of rough can cost $7 to $12 per pound depending upon the quality of color and suitability for tumbling.
|Pieces of green, yellow and reddish-orange aventurine tumbling rough from India. These pieces of rough average about 1 inch across. This material costs between $5 and $10 per pound and is shown wet.
|Photos of black basalt cobbles before and after tumbling. Surprising change? They were purchased in a 40 pound bag from Home Depot lawn and garden center for $4.99. Some catalogs sell them as "massage stones" for a few dollars each, but you can make them for about 25 cents.
|A nice colorful assortment of landscape glass. This material is often available at lawn and garden supply stores. You can get a big bag for just a few dollars and it makes beautiful tumbled stones. Some people polish it to a bright luster and other people like it with a frosted finish.
|Igneous and metamorphic rocks from Ohio River gravels that have been polished in a rock tumbler. The gravels are a popular landscaping material in the Pennsylvania, Ohio, West Virginia area.
|Lake Superior agate is a favorite tumbling rough. These nodular agates are found in the Great Lakes region and were transported from the north by glaciers during the Great Ice Age. These are small nodules of average quality, mostly less than one inch in size. Material like this costs a few dollars per pound.
| Don't try to tumble rocks with protrusions, voids or fractures. They usually don't tumble well and they often break during one of the final steps and scratch every other rock in the barrel. These rocks are not suitable for rock tumbling. Discard them or break them into smaller pieces.
| Rocks and Minerals Commonly Tumbled