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 and use up costly grits and polishes, 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 below 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
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 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.
To break a rock, place it on a hard surface that is okay to damage. An old brick or another rock works nicely (don't do it on a sidewalk or concrete porch - you will damage the surface). Put the rock under a piece of heavy cloth and strike it with the hammer. The heavy cloth will help prevent shards from flying. Some people recommend using an old sock for this but a sock will not last very long if you have a lot of rocks to break.
Additionally, if some rocks have pits, protrusions, deep cracks, or a large amount of concave surface area, it would be best to break them. Above are some examples of rocks that should be broken. 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 below. 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.
Commonly Tumbled Quartz Varieties
- Jasper
- Agate
- Tiger Eye
- Amethyst
- Aventurine
- Carnelian
- Rose Quartz
- Petrified Wood
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Other Commonly Tumbled Materials
- Malachite
- Hematite
- Obsidian
- Lapis Lazuli
- Turquoise
- Moonstone
- Amazonite
- Opal
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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 rock in lots of one pound or more. These lots 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. 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 in one of these types of areas it still possible to enjoy tumbling by purchasing the rough materials or looking for them while on vacation. Although the joy of finding your own tumbling rough can be very rewarding, it can often be much more economical to purchase rough rocks than hunt for them.
