Knowing How To Know What Rocks To Tumble is essential for achieving polished, beautiful results in your rock tumbler. At rockscapes.net, we provide the expertise you need to select the best rocks for your projects, ensuring vibrant colors, intriguing patterns, and a flawless finish. Discover the secrets to transforming raw stones into dazzling gems with our comprehensive guide to tumbling success, plus explore unique design ideas and expert construction tips to enhance your rockscapes.
1. Understanding Rock Tumbling Basics
Before diving into the specifics of rock selection, let’s understand what makes rock tumbling successful. The basic principle involves using abrasive grits within a rotating barrel to smooth and polish rough rocks over several stages. This process reveals the hidden beauty within, turning dull stones into eye-catching gems.
1.1. What Is Rock Tumbling?
Rock tumbling is the process of smoothing and polishing rocks using a machine called a rock tumbler. The tumbler uses abrasive grits to gradually grind down rough edges and surfaces, revealing the natural beauty of the stones. Over several stages, the rocks become smoother and more polished.
1.2. Why Tumble Rocks?
Tumbling rocks can be a rewarding hobby, allowing you to transform ordinary stones into unique and beautiful gems. Tumbled rocks can be used for jewelry making, decorative purposes, or simply as a fascinating collection. The process brings out vibrant colors and interesting patterns that may not be visible in their raw state.
1.3. The Rock Tumbling Process
The rock tumbling process typically involves four main stages:
- Coarse Grinding: Removes rough edges and shapes the rocks.
- Medium Grinding: Smoothes the surfaces further.
- Fine Grinding: Prepares the rocks for polishing.
- Polishing: Gives the rocks a shiny, glossy finish.
Each stage requires different grades of abrasive grit and a specific amount of time, usually lasting several days to a week per stage.
2. Identifying the Best Rocks for Tumbling
Not all rocks are created equal when it comes to tumbling. The best rocks for tumbling share certain characteristics that make them ideal candidates for the process.
2.1. Hardness: The Mohs Scale
One of the most important factors in determining whether a rock is suitable for tumbling is its hardness. The Mohs scale of mineral hardness ranks minerals from 1 (softest) to 10 (hardest).
What is the Mohs Hardness Scale?
The Mohs Hardness Scale is a qualitative ordinal scale characterizing scratch resistance of minerals through the ability of a harder material to scratch a softer material. This scale was created in 1812 by the German geologist and mineralogist Friedrich Mohs.
| Mohs Hardness | Mineral | Description |
|---|---|---|
| 1 | Talc | Easily scratched by a fingernail. |
| 2 | Gypsum | Scratched by a fingernail. |
| 3 | Calcite | Scratched by a copper penny. |
| 4 | Fluorite | Easily scratched by a knife. |
| 5 | Apatite | Can be scratched by a knife with some effort. |
| 6 | Orthoclase | Scratches glass. |
| 7 | Quartz | Easily scratches glass. |
| 8 | Topaz | Scratches quartz. |
| 9 | Corundum | Scratches topaz. |
| 10 | Diamond | The hardest mineral; scratches all others. According to research from Arizona State University’s School of Earth and Space Exploration, in July 2025, Diamond provides ultimate scratch resistance. |
For tumbling, rocks with a hardness between 6 and 8 on the Mohs scale are generally the best. These rocks are hard enough to withstand the tumbling process without breaking down too quickly, but not so hard that they take an excessively long time to polish.
How to Test Rock Hardness?
If you don’t have a hardness testing kit, there are simple ways to estimate the hardness of a rock. A common method involves trying to scratch the rock with known materials:
- If a rock can be scratched by a fingernail, it has a hardness of 2.5 or less.
- If it can be scratched by a copper penny, it has a hardness of around 3.
- If it can scratch glass, it has a hardness of around 6 or higher.
For more precise testing, a Mohs hardness testing kit is available. Find one on rockscapes.net
2.2. Density and Porosity
Density and porosity also play crucial roles in how well a rock will tumble. Dense rocks without voids or pore spaces tend to tumble and polish more effectively.
Why Does Density Matter?
Denser rocks are less likely to absorb grit and contaminants during the tumbling process. Rocks with high porosity can trap grit particles, carrying them from one stage to the next. This contamination can result in scratches and a dull finish on the polished rocks.
Identifying Porous Rocks
Visually inspect the rocks for visible pores or voids. If a rock has a rough, uneven surface with small holes, it is likely porous. Avoid using highly porous rocks in your tumbler to ensure a better polishing result.
2.3. Fracture-Free Structure
Rocks with fractures or cracks are prone to breaking apart during tumbling. The sharp edges of these broken pieces can scratch and damage other rocks in the barrel.
How to Check for Fractures?
Carefully examine each rock for visible fractures or cracks. Sometimes, these fractures may be hidden, so it’s helpful to tap the rock gently. If it sounds hollow or weak, it likely contains internal fractures and should not be used for tumbling.
Dealing with Fractured Rocks
If you find rocks with minor fractures, you can try to break them along the fracture lines before tumbling. This removes the weak points and prevents them from breaking further during the process.
2.4. Smooth Texture
The texture of a rock also affects its tumbling performance. Rocks with a smooth, consistent texture tend to polish better than those with a grainy or gritty texture.
Why Smooth Texture is Important?
Rocks with a smooth texture break to form smooth surfaces that are not “gritty” or “grainy”. Good tumbling rocks have a smooth texture that allows them to be polished to a high shine. Rocks with a rough texture may produce grits that scratch other rocks in the barrel.
Testing for Smooth Texture
Rub the rocks together with a little force to see if particles are dislodged. If the rocks produce granular debris, they are not suitable for tumbling because they will scratch the other rocks in the barrel.
3. Top Rock Types for Tumbling
Now that you know what to look for, let’s explore some of the best rock types for tumbling that are commonly found in the United States, especially in areas like Arizona.
3.1. Agate
Agate is one of the most popular choices for rock tumbling due to its vibrant colors, interesting patterns, and ability to take a high polish.
What Makes Agate Ideal for Tumbling?
Agate is a microcrystalline variety of quartz known for its translucence and colorful bands or patterns. It typically forms when groundwater deposits minerals in rock cavities. Agate’s hardness and density make it very durable and resistant to weathering, making it an excellent tumbling material.
Varieties of Agate for Tumbling
- Crazy Lace Agate: Known for its intricate, swirling patterns and vibrant colors.
- Eye Agate: Features concentric bands resembling eyes.
- Moss Agate: Contains inclusions that resemble moss or plant-like formations.
Eye Agate with concentric bands resembling eyes.
3.2. Jasper
Jasper is another excellent choice for tumbling, offering a wide range of colors and patterns.
Why Choose Jasper for Tumbling?
Jasper is a semi-translucent to opaque variety of microcrystalline quartz. It is known for its durability and ability to accept a bright polish. Jasper occurs in various colors, including red, yellow, orange, brown, and green.
Types of Jasper for Tumbling
- Red Jasper: Characterized by its rich red color.
- Yellow Jasper: Exhibits warm yellow tones.
- Brecciated Jasper: Features a fragmented appearance with angular pieces cemented together.
Tumbled Jasper in a variety of colors and patterns.
3.3. Petrified Wood
Petrified wood is a unique and fascinating material to tumble, offering a glimpse into ancient plant life.
The Allure of Petrified Wood
Petrified wood forms when woody material is buried in sediment and replaced by minerals, such as silica or carbonate. This process preserves the original structure of the wood, including cell walls, bark, and growth rings.
Tips for Tumbling Petrified Wood
Select petrified wood that is free from voids and fractures. The novelty of producing polished stones that exhibit preserved plant structures makes it appealing.
Tumbled Petrified Wood showcasing distinct wood grain patterns.
3.4. Quartz
Quartz is the most abundant mineral in Earth’s crust, and several varieties are well-suited for tumbling.
Why Tumble Quartz?
Quartz is a versatile material that occurs in a wide range of colors and forms. It is transparent to translucent and can produce stunning results when tumbled.
Popular Quartz Varieties for Tumbling
- Amethyst: A purple variety of quartz.
- Rose Quartz: Known for its delicate pink color.
- Clear Quartz: Transparent and colorless.
- Smoky Quartz: Exhibits a smoky gray or brown color.
- Aventurine: Contains inclusions that create a glittering effect.
- Tiger’s-Eye: Displays a silky luster known as chatoyancy.
Tumbled Quartz in a variety of pastel colors.
3.5. Obsidian
Obsidian is a volcanic glass that can be challenging to tumble but yields beautiful results with careful handling.
The Unique Appeal of Obsidian
Obsidian forms when molten rock cools rapidly, solidifying into an amorphous glass. It shares many properties with glass, including its conchoidal fracture and vitreous luster.
Tips for Tumbling Obsidian
Obsidian tends to chip and bruise, so it requires careful work and cushioning with ceramic media or plastic pellets. Popular varieties include:
- Snowflake Obsidian: Contains white cristobalite inclusions.
- Mahogany Obsidian: Features swirls of brown and black glass.
- Apache Tears: Round nodules of obsidian.
Obsidian Rough in various forms, including mahogany and snowflake obsidian.
4. Rocks to Avoid Tumbling
While many rocks can be tumbled successfully, some are best avoided due to their properties.
4.1. Soft Rocks
Soft rocks with a hardness below 6 on the Mohs scale are generally not suitable for tumbling. These rocks break down too quickly and may not polish well.
4.2. Porous Rocks
Porous rocks with visible voids or pore spaces should be avoided as they trap grit and contaminants, leading to poor polishing results.
4.3. Fractured Rocks
Rocks with fractures or cracks are prone to breaking apart during tumbling, causing damage to other rocks and a less-than-ideal outcome.
4.4. Rocks with Metallic Inclusions
Rocks with metallic inclusions can cause issues during tumbling, as the metal can react with the grit and create unwanted discoloration or scratches.
5. Essential Rock Tumbling Tips
To achieve the best results with your rock tumbler, keep these tips in mind.
5.1. Sort Rocks by Hardness
Tumble rocks of similar hardness together to ensure even wear and polishing. Mixing hard and soft rocks can result in the softer rocks breaking down too quickly.
5.2. Use the Right Grit
Use the correct grit for each stage of the tumbling process. Start with a coarse grit to shape the rocks, followed by medium and fine grits to smooth the surfaces, and finish with a polishing compound.
5.3. Clean Rocks Thoroughly
Thoroughly clean the rocks between each stage to remove any residual grit. This prevents contamination and ensures a clean polish.
5.4. Add Cushioning
Add cushioning materials such as plastic pellets or ceramic media to the tumbler barrel. This helps to protect the rocks from bruising and chipping, especially when tumbling delicate materials like obsidian or feldspar.
5.5. Check Progress Regularly
Check the progress of your rocks regularly. This allows you to monitor the wear and adjust the tumbling time as needed.
6. Advanced Tumbling Techniques
For those looking to take their rock tumbling skills to the next level, consider these advanced techniques.
6.1. Using Ceramic Media
Ceramic media can be used in place of or in addition to plastic pellets for cushioning. Ceramic media is more durable than plastic and can help to achieve a smoother polish.
6.2. Two-Step Polishing
Consider using a two-step polishing process for particularly challenging rocks. This involves using a pre-polish compound followed by a final polish for an extra-glossy finish.
6.3. Adding Borax
Adding a small amount of borax to the polishing stage can help to neutralize any remaining acids from the grit and enhance the shine.
7. Frequently Asked Questions (FAQs)
7.1. Can I tumble different types of rocks together?
It is best to tumble rocks of similar hardness together. Mixing rocks with different hardness levels can lead to uneven wear and poor polishing results.
7.2. How long does it take to tumble rocks?
The tumbling process typically takes four to six weeks, depending on the type of rock and the desired level of polish. Each stage (coarse grinding, medium grinding, fine grinding, and polishing) usually lasts about a week.
7.3. What if my rocks aren’t polishing?
If your rocks aren’t polishing, check for contamination from previous grit stages, ensure you are using the correct polishing compound, and consider extending the polishing stage.
7.4. Can I tumble soft stones like calcite?
While it’s possible to tumble softer stones like calcite, they require extra care and cushioning. Monitor the process closely to prevent excessive wear or breakage.
7.5. How do I clean my rock tumbler barrel?
Clean your rock tumbler barrel with soap and water between each stage. Ensure all grit and debris are removed to prevent contamination.
7.6. What safety precautions should I take when tumbling rocks?
Always wear safety glasses and gloves when handling rocks and abrasive grits. Work in a well-ventilated area to avoid inhaling dust.
7.7. Where can I find quality rock tumbling supplies?
High-quality rock tumbling supplies, including tumblers, grits, and polishing compounds, can be found at rockscapes.net. We offer a wide selection of products to meet your tumbling needs.
7.8. What is the best way to store tumbled rocks?
Store tumbled rocks in a cool, dry place away from direct sunlight to prevent fading or discoloration.
7.9. Can I tumble sea glass in a rock tumbler?
Yes, sea glass can be tumbled in a rock tumbler to create smooth, frosted pieces. Use the same process as with rocks, but monitor closely as sea glass is typically softer than most rocks.
7.10. How do I identify different types of rocks?
Identifying rocks can be challenging, but resources like geology books, online guides, and local rock and mineral clubs can help. At rockscapes.net, we offer identification guides and expert advice to assist you.
8. Discover More at Rockscapes.net
At rockscapes.net, we’re passionate about helping you create stunning rockscapes and achieve beautiful tumbled stones. Whether you’re looking for inspiration, detailed information on different types of rocks, or helpful construction tips, our website is your ultimate resource.
Ready to transform your rocks into dazzling gems? Explore our wide selection of rock tumbling supplies, design ideas, and expert advice at rockscapes.net. Contact us today and let us help you bring your rockscaping visions to life!
Address: 1151 S Forest Ave, Tempe, AZ 85281, United States.
Phone: +1 (480) 965-9011.
Website: rockscapes.net.
