Updated formulas are presented for estimating the weights of mounted colored gemstones. These formulas are derived from measurements and weights of thousands of German-cut calibrated amethysts and citrines, representing most commercially available shapes and sizes. As with the formulas taught by GIA, the dimensions of a stone are multiplied by its specific gravity and by a “shape factor” that is determined by the stone’s face-up outline. This article also illustrates how the shape factor changes over a continuum of common face-up outlines. As in previous formulas, a separate weight correction factor is applied to stones that show proportion variations in profile view.
Updated formulas are presented for estimating the weights of mounted colored gemstones. These formulas are derived from measurements and weights of thousands of German-cut calibrated amethysts and citrines, representing most commercially available shapes and sizes. As with the formulas taught by GIA, the dimensions of a stone are multiplied by its specific gravity and by a “shape factor” that is determined by the stone’s face-up outline. This article also illustrates how the shape factor changes over a continuum of common face-up outlines. As in previous formulas, a separate weight correction factor is applied to stones that show proportion variations in profile view.
