The amount of mineral loss depends on several factors, such as the type and hardness of the stones, the size and shape of the barrel, the amount and quality of the grit and polish, the speed and duration of the tumbling, and the desired finish of the stones. Generally the softer it is (lower mohs), the more wastage you'll see under the same tumbling conditions.
The average mineral loss for tumbling gemstones is about 10-20% of the original weight.
