Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:2648659.

These are some gems I made, I've printed some of these up to 5 inches across. Most can be printed completely hollow. However gem 4 may need some infill, depending on the number of top layers.

I printed all mine with 0.8mm wall thickness and because of the 45 degree angles this seems to result in the model being quite strong.

Layer height is up to you and the size you print.