Testing IOR of 2.417 in Blender material, rendered in YafaRay Direct lighting with HDRI environment.

UPDATE (March 10, 2016):

Software: Blender 2.76b
Here’s a new render sample from the new YafaRay render engine, YafaRay-E v2.1.1.
Somehow, the old YafaRay Blend file doesn’t render, and the affected settings are the World, and the Area lights. Anyway, the conversion was easy.

Blend File: Diamonds Blender File

Sample render from YafaRay-E v2.1.1: