What Is the Best Grit for Stage One of Rock Tumbling?

Rock tumbling is a rewarding hobby that transforms rough stones into beautifully polished gems. One of the most important decisions you will make in the tumbling process is choosing the correct grit—especially for stage one, where most of the shaping happens. In this article, we answer the key question: what is the best grit for stage one of rock tumbling?

Whether you are a beginner or looking to improve your results, understanding rock tumbling grit will dramatically improve your tumbling success.

Understanding the Rock Tumbling Process

Before choosing the best grit, it helps to understand how rock tumbling works. Most tumbling processes are divided into four main stages:

  • Stage One – Coarse Grind (Shaping)
  • Stage Two – Medium Grind (Smoothing)
  • Stage Three – Fine Grind (Pre-polish)
  • Stage Four – Polish

Stage one is the foundation of the entire process. Mistakes made here are difficult—if not impossible—to fix later.

Why Stage One Grit Is So Important

Stage one removes sharp edges, cracks, and surface flaws from rough rock. It is where rocks are rounded and shaped, not polished. Using the wrong grit at this stage can lead to:

  • Poor shaping
  • Cracks that reappear later
  • Longer tumbling times
  • Unsatisfactory final polish

Choosing the correct coarse grit ensures your stones progress smoothly through later stages.

What Is the Best Grit for Stage One of Rock Tumbling?

The Best Grit: F80 Grade Silicon Carbide

This grit size is considered ideal because it balances effective material removal with controlled shaping, making it suitable for most types of tumbling rough.

Why F80 Grit Is Ideal for Stage One

1. Effective Shaping Power

F80 grit is coarse enough to grind away rough surfaces, sharp edges, and fractures efficiently.

2. Durable and Long-Lasting

Silicon carbide breaks down slowly during tumbling, maintaining its cutting ability over time.

3. Suitable for Most Rocks

This grit works well for common tumbling materials such as:

  • Agate
  • Jasper
  • Quartz
  • Chalcedony
  • Petrified wood

Can You Use Other Grits for Stage One?

While F80 grit is best for most situations, alternatives may be used in specific cases. 60/90 grit is a common suggestion, but is generally easier to obtain in the USA. In the UK, F80 grade silicon carbide is the standard stage one grit for rock tumbling. 

Using coarser grits for stage one can have advantages, if you know what you're doing. F20 silicon carbide is available and can work for larger or much rougher stones, as it removes material much faster. That being said, the coarser grit does have higher risk of leaving deep scratches, so not something we'd suggest for beginners just starting out. 

How Much Grit Should You Use in Stage One?

A common guideline is 1 tablespoon of F80 grit per 500 g (1 lb) of rocks. Always ensure your tumbler barrel is filled two-thirds to three-quarters full with rocks and water just covering the stones.

How Long Should Stage One Last?

Stage one typically takes 7 to 10 days, but many rocks benefit from multiple stage-one cycles. Do not rush this step—stones should be:

  • Smooth to the touch
  • Free of sharp edges
  • Properly rounded

If necessary, repeat stage one with fresh F80 grit until the stones are ready.

To achieve well-shaped, high-quality tumbled stones, F80 silicon carbide grit is the best grit for stage one of rock tumbling. It provides the perfect balance of cutting power, durability, and control, making it ideal for beginners and experienced rock tumblers alike.

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