1ct Morganite (Oval, 8.63×5.75mm, Light Red) vs 1.2ct Diamond (Oval, 8.63×5.75mm, White)

All things being equal, Diamond will face-up smaller than Morganite for a given carat weight, because it has higher specific gravity (3.52 vs. 2.8 - this means it's "heavier" compared to Morganite of the same size).i Face-up size also depends heavily on the proportions of the cut.

Face-up area is a measure of the size of the gem when viewed from above (as set in a ring). It tells you how big the gem is at the girdle plane.