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While nature can certainly create some stunning rock formations, recovered rocks are initially quite different from those displayed in stores and collections. There is an entire process that rough rocks go through in order to become the shiny, magnificent, and desirable stones seen by the public.
Agate, Jasper, Quartz, Aventurine, Tiger’s Eye, Obsidian, Howlite, Petrified Wood, Amazonite, Moonstone, Sunstone, Labradorite, Sodalite, Unakite, and Dalmatian Stone are good rocks for tumbling. This is due to their density, Mohs hardness, and physical properties.
Some rocks don’t have ideal physical properties for rock tumbling, but there are many rocks that are perfect for this process. This article lists some of the best rocks for tumbling, and details which qualities are required for tumbling to ensure you end up with some gorgeously glossy stones.
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What Rocks and Minerals are Good for Tumbling?
There is something incredibly satisfying about witnessing such a drastic transformation, and the process by which a rough rock is transmuted into a smooth shiny stone gives many people an abundant sense of achievement.
Apart from having the joy of owning a lovely collection, this accomplishment is often the main motivation for this hobby.
High-quality rough rocks are needed in order to achieve high-quality results. Rocks that are permeable or cracked will not produce an attractive tumbled stone.
Low quality or granular textured rocks also have a chance of shedding fragments and scratching surrounding rocks, so these are carefully modified beforehand or avoided completely.
The rock tumbling process is understandably harsh on the rocks, and it’s therefore crucial that the rocks have durable physical properties to withstand the process.
Other than the overall quality of the rock, one of the most important factors when selecting rocks to tumble is its hardness.
Most tumbler grit is made of silicon carbide, one of the hardest artificial materials, and the selected rocks need to withstand this.
The entire batch of rocks going into the tumbler barrel also needs to be similar in hardness, as a large difference in hardness could result in the softer rocks being damaged.
A batch of softer rocks can be used, but the timing of each stage will need to be shortened and should be more carefully monitored.
A batch of rocks that are too hard will result in the opposite effect, and it will take extremely long to smooth down. For very hard batches, the coarse grit stage is often prolonged for the best results.
In addition, factors like consistency and quality also have an impact on potential outcomes. As a result of these conditions, the most ideal tumbling rocks do not have fractures, voids, or wide pores, but are dense, smoothly textured, and have a Mohs hardness of around 7. These rocks are the best options to achieve great results.
Agate is a microcrystalline variation of quartz and is undoubtedly the most popular option for tumbling. This is due to its hardness, density, natural smoothness, how commonly it is obtained, and how well the rock responds to the tumbling and polishing process.
It generally forms when groundwater deposits minerals in rock cavities, in fractures, and in bedding plane separations. It can therefore be found in abundance around stream beds and dry washes in some geological locations.
This translucent material carries an array of interesting visual qualities including eyes, bands, cloudy spotting, spirals, and various colorful patterns.
Its unique interior glow coupled with its translucence and patterns gives this rock a bright, distinctive, and aesthetically pleasing appearance once polished.
Agate is one of the best options for tumbling, as each rock is exclusive, making it easy to build up a visually diverse tumbled rock collection.
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Jasper is another variety of microcrystalline quartz and is exceptionally popular due to its wide range of colors, durability, and density.
It can range from opaque to semi-translucent, and forms in various fracture fillings and replacements.
This beautiful rock occurs in an array of monotone colors such as white and shades of grey. It also forms in earthy tones like red, yellow, orange, and brown. This color palette is complemented by the rock’s swirls, spirals, and clouds of contrasting tones.
It is relatively hard and quite suitable for the tumbling process. The natural undertones of the rock create a lovely foundation for bright and lustrous polishing, and the use of Jasper could result in a large visual variety in your collection.
Quartz is the most plentiful mineral resource that forms within the Earth’s crust and comes in a variety of variations. Some of the most commonly used types of crystalline quartz include amethyst, clear, white, rose, yellow, and smoky quartz.
These kinds of quartz are ideal for tumbling, as they are hard, durable, and relatively easy to smooth down. Quartz ranges from transparent to translucent and receives bright polish extremely well.
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This is a variety of quartz that commonly forms in green tones, is a particularly popular option for rock tumbling, and is sought after by jewelry makers. It is dense and durable for the tumbling process and has a range of interesting visual qualities.
Aventurine contains inclusions of mica, iron oxide, or other minerals which produce a different effect as opposed to other quartz variations.
The presence of these minerals has a special orientation which results in a shimmery, glittering appearance when observed from particular angles.
Tiger’s eye is another popular tumbling material due to its suitable physical properties. The rock is similar to other quartz variations but forms when crocidolite is replaced by quartz.
This results in a rock that is fibrous in texture, and it intermingles with surrounding light to create a silky luster known as chatoyancy.
This volcanic rock often occurs in the margin of the lava flow and has been a miraculous enigma for the public since it was discovered.
It’s formed when molten lava rock material cools so rapidly that it solidifies into a shapeless glass form as opposed to crystalizing into structured mineral forms as other rocks do.
Obsidian is not as easy to tumble as other rocks such as quartz. This is due to the fact that it has a Mohs hardness of 5 – 6 instead of around 7, which could result in bruising and chipping during the tumbling process.
However, with the use of ceramic media or plastic pellets for cushioning, and some adjustments in tumble timing, you could end up with a stunning dark stone in an array of black, brown, red, and other dark tones.
The swirls and nodules are reminiscent of its molten lava origins, and some specimens called ‘snowflake obsidian’ feature white cristobalite spherulites giving it a black-and-white spotted appearance.
Howlite is another suitable rock for tumbling. The hardness and density make it an ideal choice for the smoothing and polishing process.
However, this rock is not as popular, as it is fairly plain and bland in appearance. Howlite usually forms in shades of white, which is seen as relatively uninteresting for most people, particularly in comparison with some of the more popular tumbling stones.
As a result of this, Howlite is still tumbled frequently but is often dyed to resemble turquoise in order to enhance its appearance.
Although this material has been named petrified ‘wood’, it is in fact a kind of rock. This rock is formed when woody material is submerged in sedimentary deposits like ash fall and is then replaced by siliceous or carbonate materials transported by groundwater. Its properties are ideal for tumbling since it’s dense and relatively smooth.
Despite the fact that petrified wood does not necessarily display a range of bright colors or patterns, it is unique in the fact that it can often display cell walls, bark, growth rings, and relative plant structures.
Petrified wood is not easy to come by, and does not have an overtly exquisite appearance. But, the originality of having a satisfyingly smooth stone that exhibits preservations of plant structures is incredibly alluring to many people.
TIP: Do you know that some pieces of petrified wood can be really valuable? And even more when it is tumbled. Find out which factors are most important for the price of petrified wood here:
Amazonite is a rock containing microcline feldspar minerals and is named after the Amazon River.
Although it is not generally found in that area, this rock forms in a variety of green shades such as pastel green, deep green, and blue-green, resembling the shades of green that run through the Amazon River.
Many rocks containing minerals from the feldspars group are ideal for tumbling, as they respond well to the smoothing and polishing process.
However, feldspars can break during tumbling due to their planes of cleavage. These can become weak points that are vulnerable to damage if the tumbling process is too rough.
Much like obsidian, the successful tumbling of these rocks can be rewarding, and the process can be assisted through the use of plastic pellets and ceramic media for cushioning.
This rock can be either an orthoclase or albite feldspar. The rock has similar physical properties to most feldspars, is relatively hard, and polishes well.
Moonstone forms in a wide variety of colors such as white, pink, grey, green, orange, and brown, each of which occurs in various shades. The stone has a natural glistening opalescent sheen and exhibits an interesting response to light known as adularescence.
Sunstone is a fascinating plagioclase variation of feldspar, and its name stems from its unique visual appearance. The mineral composition of sunstone includes minuscule copper flakes, which cause an interesting effect when moved under the light.
This is due to the special orientation of the copper flakes which reflect light within the stone, resulting in a copper-colored flash. If tumbled carefully according to feldspar requirements, this sought-after rock could be a novelty treasure.
Labradorite is another variation of plagioclase feldspar that is a popular option for rock tumbling. This is due to the effect that its natural qualities have when brightly polished.
The rock displays the phenomenon known as labradorescence, which describes a specific reaction to light. The mineral composition of this material results in a play of colors including shades of electric blue, green, and yellow when moved under the light.
Although sodalite is rare, it’s valued for its hardness, durability, and beautiful sheen when polished. It has a Mohs hardness of approximately 6, which is still fairly suitable for the tumbling process.
The rock frequently exhibits white patterns formed by other minerals distributed in the rock such as nepheline. These white swirls complement its rich blue color.
This distinctive igneous rock has been named after the Unaka Mountains in North Carolina, where the stone has been quarried since the mid-1990s.
Unakite is very unique in appearance, as it is made up of pink and green mineral grains. Its combination of orange, pink, yellow, and green mineral grains makes up its final visual qualities.
Unakite contains orthoclase, an orange-pink mineral of the feldspar group which has a Mohs hardness of 6, making it a suitable option for rock tumbling. The yellow-green mineral is called epidote, which is a rare mineral found in a low amount of igneous rocks.
Also known as Dalmatian jasper, this rock is a monochrome igneous rock found in Chihuahua, Mexico. Although this rock is not a type of jasper, the name stems from its appearance, as it resembles the spots of a Dalmatian dog. It was thus later renamed as Dalmatian stone.
These rocks form in a range of neutral shades from light brown to bright white, with varying sizes of black spots.
It’s an extremely popular rock for many people who are beginning rock tumbling as a hobby, as it tumbles quickly, forms a desirable rounded shape in the tumbler, and polishes well into a subtle level of luminosity.
Can You Put Crystals in a Rock Tumbler?
You can definitely tumble crystals. But it’s still important to understand crystal properties in order to have a successful tumble batch, as they differ from rocks.
A crystal is a solid mass that has an organized structure, with very particulate positioning and repeating arrangement of atoms that form a three-dimensional pattern known as crystal lattice.
Crystals are present in many solids, but are often cryptocrystalline or microcrystalline, making it a microscopic contributing factor to the formation, as opposed to a macrocrystalline crystal that is visible to the naked eye.
A crystalline structure is what makes a true crystal identifiable since it’s unique and specific to each mineral variety.
Rocks are usually composed of at least two varying minerals, and these rock-forming minerals can create igneous, sedimentary, and metamorphic rocks.
Since rocks are made up of minerals as opposed to crystals, they do not have a crystalline structure. Some of the most popular crystals include Amethyst, Azurite, Celestite, Citrine, Fluorite, Garnet, Malachite, Pyrite, and Rhodochrosite.
Many cryptocrystalline and microcrystalline variants of Quartz are debatable ‘crystals’ as well. All of these can be tumbled, but each crystal will need to be quality checked carefully, and may require some adaptions to the process for the best results.
BTW: Do you want to know more about rock and mineral identification? The books listed below are the best ones you can find on the internet (Amazon links):
- Smithsonian Handbooks: Rocks & Minerals
- Gemstone & Crystal Properties (Quick Study Home)
- Ultimate Explorer Field Guide: Rocks and Minerals (National Geographic Kids)
How Much Grit Do You Put in a Rock Tumbler?
Rock tumbling involves the use of a rock tumbler, water, and tumbler grit varying in coarseness. Combined with water and the motion of the rock tumbler barrel, this grit scratches the surfaces of the rocks resulting in smooth, rounded edges and surfaces.
This process consists of five stages – coarse grind, medium grind, fine grind, polishing, and burnishing. Different types of tumbler grit are used in each of the grinding stages, and it’s crucial to ensure that the correct grit is present in each corresponding stage.
Each rock, the tumbler barrel, and all tools are cleaned between each stage to avoid cross-contamination of grit, rock particles, and granules.
In each tumbling stage, two tablespoons of grit are used for each pound of rock – first coarse, then medium, then fine grit. Within the polishing stage, the grit is replaced with rock polish, and ivory bar soap is used within the burnishing stage.
It’s therefore essential to weigh the rocks before tumbling in order to calculate the required amount of grit, rock polish, and ivory bar soap for each stage within the rock tumbling process.
Can You Tumble Rocks without a Tumbler?
The process itself is more time-consuming than difficult, as various types of machines are generally used, namely rock tumblers, and different kinds of rotary tumblers.
However, it’s still possible to create beautifully polished rocks and gemstones without the machinery.
You can smooth down and polish rocks by hand using a bucket, hot water, soap, old toothbrush, protective eyewear, gloves, handheld rotary tool, stone polish, and of course the rough rocks.
You will also need coarse, medium, fine, and ultra-fine sandpaper to replace the grit used in a tumbler.
This can be done by imitating the traditional rock tumbling stages, cleaning the stones by hand, and grinding the stones in a handheld rotary tool.
The rocks will need to be individually sanded down with moistened sandpaper which is compatible with the hardness of your rock, and stage of smoothness. They will need to then be polished by hand using a heavy fabric such as denim until they begin to shine.
There are plenty of popular and suitable options for rock tumbling, all of which require knowledge and an abundance of patience. Some of these rocks are more easily attainable, and some require a slightly different approach to the tumbling method.
Regardless, the achievement and reward at the end of the process are invaluable, and being able to hold these smooth, glistening treasures under twinkling lights will certainly make the process worth it.
TIP: Actually, I wrote a step-by-step guide on how to tumble rocks without a rock tumbler. Find out how to do it in the article below: