What Size Gems Can I Expect?

The ratio of final polished gem weight to original rough stone weight is called the yield. The first thing one must understand when predicting yield is that the entire shape of the gem must fit inside the shape of the rough piece. During cutting, material can be taken away, but it can never be added back.

In a round or rectangular piece of rough, at least half of the stone must be removed to yield the pyramid shape of the gem's pavilion. In less perfectly shaped stones, it may be necessary to remove as much as 90 percent of the stone's total mass to realize a gem of decent quality. Both of these extremes are uncommon, and the rule of thumb is to expect that the finished gems will weigh about 1/5 to 1/4 the weight of the original rough.

Second, nearly all rough gemstones have inclusions which may or may not be easily visible. When the gem is examined by our expert faceters, it may be found that the rough must be sawed into smaller pieces to remove or hide unsightly inclusions. This is often done when a stone has a few major inclusions, but has regions that can be faceted to the desired clarity. Overall yield and quality can be improved this way, but the resulting gems may be smaller than expected.

The first step in faceting gems is to saw the stone into roughly the shape of the final gem. This process is called preforming, and produces a stone that is roughly the shape and size of the finished gem. The trimmings are much smaller pieces of stone that may themselves be faceted. Unless instructed otherwise, these small pieces will be faceted into gems as small as one or two millimeters, improving the overall yield and providing you with small stones suitable for cluster settings or accents.