Gemstones have a base reflectance of 16%, so Specular is set to 2 and I set Transmission to 1. I've played around with varying the colour, roughness and IOR (there are many examples online, here is one). I also tried adding a little Transmission Roughness to a couple of stones - to enable that the Distribution must be changed to GGX instead of the default Multiscatter GGX.

The mesh is a primitive from Lightwave, there is a single infinite light and I've used a jpg panoramic sky plus simple reflective surface for the Ground.

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