How to polish rocks

If you've ever been to the beach, you've probably picked up rocks that are perfectly smooth and rounded.

The ocean is a natural rock tumbler: as rocks are rolled by the waves and rubbed against sand and each other, their rough edges and corners are filed away.

A rock tumbler can mimic this process and even take it a step further by adding polish to make the stones shine. Rock tumblers work much faster (4-6 weeks) than the ocean because their motion is constant and they use an abrasive substance called silicon carbide, which is much harder than sand.

Lapidary is the art of cutting and polishing gemstones. Rocks and minerals come in all different colors and patterns, and polishing them to a smooth shininess brings out their incredible beauty. Polished rocks are often used in jewelry. What You Need: Rocks, Rock tumbler, 4-stage polishing grit Selection: When selecting rocks to polish in a tumbler, there are several things to consider: Size: You should include a mix of sizes in your tumbler, from 1/4″ to 1″.

The smaller stones rub up against all the contours of the bigger stones, ensuring a uniform shaping.

Hardness: All the rocks in a batch should be around the same level on the Mohs hardness scale.

The scale runs from 1 (talc) to 10 (diamond) and at each level a mineral can be scratched by something of the same or higher level, but nothing lower.

If you tumble rocks of different hardness, the softer ones will be worn down too much and the harder ones not enough.

If your rocks scratch each other equally, they are around the same hardness.

The ideal hardness for tumbling is between 5-7. You can test the hardness level of your rocks using a set of Mohs minerals, or by trying to scratch them with a pocket knife (hardness 5.5) or a steel file (6.5).