Tumbled stones also known as crystals are rocks and minerals that have been smoothed, shaped and polished in a rock tumbler. With them being natural stones minor anomalies or "imperfections" are not uncommon. Due to the way they're produced it's rare for any two crystals to be the same.
Tumbled stones can also be cut and polished by hand. Stones produced in this way tend to be a similar size. Their shape is mostly round, oval or similar to a dice. Despite not having been produced in a rock tumbler they're still known as tumbled stones.