I was just studying your buying guide for OR sunstones and noticed something counterintuitive. Usually, larger stones cost more $/carat than smaller ones. But in the cases of some types of these stones, the reverse was true. One type, med-deep red stones w/o schiller up to 2.5 ct. were $256/ct, while 2.5 - 5 ct stones were $156/ct. What accounts for such a steep reversal in prices? Are these prices simply taken from stones announced for sale, or is their a rationale for the pricing?
Larger stones don’t always cost more per carat. In some cases, there is just less demand for larger size stones for jewelry use/greater demand for stones in specific sizes. We have more information on carat pricing in general here.
In the case of Oregon Sunstones, there are even more fluctuations due to the availability of stones in specific sizes and the popularity of specific colors. Some stones decrease in cost per carat in mid-size ranges only to increase in larger sizes (like blue-green stones with mid-deep tones) and some have higher cost per carat in mid-size ranges but lower in smaller or larger sizes (like the mystique variety).
So, in general, stones in sizes popular for jewelry will cost more per carat, and specifically, the availability of stones in specific sizes and popularity of specific colors/effects will also affect price per carat.