What are Tumbled Stones, How are they Made?

Tumbled Stones Produced in a Rock Tumbler

Tumbled stones are small pieces of a rock or mineral that have been smoothed, rounded and polished.

The process begins when rough pieces of stone of a similar shape and size are put in a rock tumbler.  The barrel is then filled with water, sand and coarse grit.

As the barrel or drum slowly rotates the stones gradually lose their rough edges and become smoother and more rounded.

The smoothness of tumbled stones is determined by the coarseness of the grit.  Initially coarse grit is used but is then replaced with medium and then fine grit.

The grit works like sandpaper.  The finer the grit the smoother the finish.

The final stage of producing tumbled stones involves them being polished.  This is done by replacing the grit with a polishing agent, usually a fine powder.

The length of time it takes to produce tumbled stones can vary from a few days to several months.  The time is dependant on several factors.  These include the size of the rock tumbler which can be a small hobby machine to something on an industrial scale.

The size and hardness of the rocks or minerals being tumbled must also be taken into account.  How full the barrel is and the coarseness of the sand or grit is also important.

Using a rock tumbler to produce tumbled stones mimics a process that takes place in nature.  When fragments of rock beneath or adjacent to a body of water are gently moved back and forth, movement caused by the motion of the water causes them to rub against each other and against sediment.

Sediment is made-up of small pieces of rock, minerals and the remains of plants and animals.

Over long periods of time rough fragments become smoother and more rounded.  Tumbled stones produced naturally are better known as as river or beach pebbles.

Most but certainly not all tumbled stones tend to be minerals.

Information about making your own tumbled stones can be found here.

Not all stones being sold as "tumbled stones" have been produced in a rock tumbler.  Some are cut from large slabs before being polished by hand.  This practice has only started fairly recently.

Stones of a similar size and shape are likely have been produced in this way.  These materials come mostly from India and other countries in Asia.  

It's quite easy to tell whether a tumbled stone has been produced in a rock tumbler by its shape.  Cube, round and oval shaped stones will not have been tumbled.  Rough stones being rotated in a drum or barrel cannot come out perfectly round, oval and they definitely won't be square.

Tumbled stones produced in a rock tumbler will rarely be exactly the same size or shape.  Stones will often have minor surface imperfections and anomalies. 
The term "tumbled stones" is now used to describe any stone that looks like a "tumbled stone" irrespective of how it's been produced.

The vast majority of "tumbled stones" are produced in South Africa, India, Pakistan and China.  Part of the beauty of stones that have been tumbled in a rock tumbler is that each piece is unique.

Stones that have been cut and polished by hand tend to have a more "perfect" appearance.

A significant amount of fake crystals, rocks and minerals are produced in China.  Tumbled stones that haven't been produced in a rock tumbler are far easier to fake.

The materials being used can be natural stone, glass, plastic, resin or any number of other materials.  Colour, texture and optical phenomenon such as sparkle or iridescence are produced or enhanced using a variety of techniques.