A tumble stone is rough rock rounded in a rotating barrel with abrasive grit and water, over weeks rather than hours. The variation between stones in a bag is not sloppiness — it is what the process does.
Weeks, not hours
Tumbling runs in stages. Coarse grit knocks the edges off over a week or more, then medium, then fine, then a polishing compound — each stage in a clean barrel, because a single grain of coarse grit carried into the polish stage scratches the whole load. Four stages, three to five weeks, and the barrel runs continuously.
That is why tumbled stones cost what they do despite being small, and why a cheap tumble polished in a rushed cycle has a slightly matte, greasy look rather than a glassy one.
Why the sizes vary
Rough rock does not break into even pieces, and softer stones lose more volume in the barrel than harder ones. A bag sold as 20–30mm will contain stones across that range and occasionally outside it. Anyone promising uniform tumbles is either hand-picking at a price, or overstating.
This is also why tumbles are sold by weight rather than count. A kilo of small stones is many more pieces than a kilo of large ones.
Named stones and mixes
A named bag — rose quartz, amethyst, tiger's eye — is sorted to one material. A mix is whatever came through, and is cheaper per kilo for that reason. Mixes are good for crafts, resin work, grids and party favours; named bags are what you want if the specific stone matters.
Be a little sceptical of very cheap "amethyst" in mixed bags. Pale purple quartz and dyed agate both circulate under the name.
What tumbles are used for
Carried in a pocket, mostly, which is the honest answer — a tumbled stone is smooth, pocket-sized and pleasant to handle, and that is a large part of why they are the most popular form of crystal sold. Beyond that: grids, jars, decorative bowls, gifts, and craft work where drilled chips are too small.
Care
Most tumbles are hard enough to be robust. The exceptions matter: selenite, calcite, halite and malachite should not be washed — selenite and halite dissolve, calcite reacts to anything acidic, and malachite contains copper and should not be soaked or handled with cut hands.
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