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Home » Rock Tumblers » Tumbling Rough

Tumbling Rough

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Quality In Means Quality Out!

Many types of rock can be successfully tumbled into stunning gems. The key point to remember in collecting, selecting or purchasing rock for your tumbler is: "Quality in means quality out!"

You will spend a lot of time tumbling the stones. You will also use a lot of electricty, grit and polish, so get the most out of your time and money by using quality rough material. Tumbling poor quality rough yields very little and the expense and time required is the same as if you tumbled top grade rock.

Pictured to the right is about three pounds of rough ready for the tumbler. These materials have been carefully selected and inspected. Pieces with voids, fractures, extremely irregular shapes or variable compositions have been either broken or discarded.

Breaking Tumbling Rough

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.

safety glasses
Impact-resistant safety glasses and gloves must be used when breaking tumbling rough!

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.

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.

More Quality Control

After you break the rocks, examine the pieces. Look for pieces that have pits, protrusions, deep cracks, or large concave surfaces. These rocks should be broken into smaller pieces or discarded as they will usually not tumble into a nice stone. To the right are some examples of rocks that should be broken - or discarded.

If a crack runs through the rock, no amount of tumbling will get it out. Break it at the start, and you can have some nice smaller gems instead. Voids that trap grit are a real problem. If they carry course grit into your fine grind or pre-polish steps those large grit grains will leave deep scratches in the rock and your work will be ruined. Discard problem rocks or break them to yield small pieces that are trouble-free.

What Types of Rock Can Be Tumbled?

A list of frequently tumbled materials is given in the table on the right. This is not a complete list - there are many other materials that can be tumbled. Lots of people who tumble become collectors and build colorful collections representing a variety of different tumbled gemstones.

An important thing to keep in mind when choosing rocks to tumble is that rocks of different hardnesses should not be tumbled together. If you do this the softer rocks will grind to tiny pieces while the harder rocks are just starting to become rounded. Check the hardness of your tumbling rough to determine which materials can be tumbled together.

The websites of many rock shops sell tumbling rough in packages of one pound or more. These packages are typically a single type of rock or many different types of rock that can be tumbled together. Experience has taught us that putting two barrels of rock through the coarse grind will yield about the right amount of rock to do the fine grind with a full load. This is because 30% of the rock or more will be ground away with each rough grind. This means that you will need to add more rocks to keep the volume optimal. Since the amount of rough that is included in some rock tumbling kits is only enough to get started, it's a good idea to buy a couple of extra pounds so that you have more rough available.

To start, you will need enough rock to fill the tumbler barrel between 2/3 and 3/4 full. Choose rocks of varying sizes, as this will promote thorough tumbling action. A batch of rocks that are approximately the same size will often not tumble properly or grind very slowly. For a 3 pound barrel, a good range of sizes is from 1/4 inch to 1 1/2 inches in maximum dimension. If your rough is too large in size, you can break the larger pieces with a rock hammer. But, be very carefull - this is dangerous work!

What Types of Rock Can NOT Be Tumbled?

Some types of rock are a waste of time to tumble if your goal is to produce nice round and shiny gemstones. Sedimentary rocks such as sandstone, coal, limestone and shale are too soft or poorly cemented to polish into shiny gems. Metamorphic rocks that contain micas or have a "grainy" texture are also unsuitable - they will break up instead of becoming smooth. And, most igneous rocks do not tumble well because they contain several different minerals that wear down at very different rates.

Perhaps you are lucky and live where agates can be found in stream beds, where quartz pebbles can be found along beaches or where large grains of interesting minerals can be taken from igneous rock outcrops. (Remember that collecting on private property without permission is unlawful and that removing rocks from parks and most other types of public land is also illegal.) If you do not live where rough tumbling rocks can be collected it still possible to enjoy tumbling by purchasing the rough materials from a rock shop or online store. You can also look for them in appropriate places while on vacation. Although the joy of finding your own tumbling rough can be very rewarding, it is often much more economical to purchase rough rocks than it is to spend gasoline and time hunting for them.

Now you are ready for Rock Tumbling Grit
high quality tumbling rough
This is a couple pounds of tumbling rough. Materials included are tigereye, brown agate, amethyst, green aventurine, rose quartz and blue quartz. .

junk in means junk out
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. Throw them away or break them into smaller pieces.

Tumbled Quartz Varieties

  • Jasper
  • Agate
  • Tiger's Eye
  • Amethyst
  • Aventurine
  • Carnelian
  • Rose Quartz
  • Petrified Wood

Other Tumbled Materials

  • Hematite
  • Obsidian
  • Lapis Lazuli
  • Moonstone
  • Amazonite
  • Common Opal
  • Granite
  • Diorite

 Rocks and Minerals Commonly Tumbled
Lapis Lazuli
Petrified Wood
Rose Quartz
Smoky Quartz
Tiger's Eye

Rock Tumbler Home Selecting A Tumbler Instructions - Part 1 Instructions - Part 2
Rotary Tumblers Vibratory Tumblers Tumbling Supplies Kid's Tumblers
Rough Grit Polish Media
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