# Which transparent mineral has the highest IOR? natural or lab made

I do apologize if this is the wrong place to ask this question. It's a rather simple question, but google gave me rather vague / random results, so I thought it might be better to ask somewhere like this place, where someone could give me a more solid answer

My question is, which mineral, regardless of its nature (mined / lab made) has the highest index of refraction.

I've heard there are ones higher than moissanite, which already has an excessively high IOR (nω=2.654 nε=2.967), but I wanted to know if there were any materials higher than that?

For those curious as to why, I just wanted to find the highest refractive material to look at. I collect rare stones and minerals, and the higher the IOR, generally the prettier the faceted stones look in the end.

• Cinnabar has higher RI values: nω = 2.905 nε = 3.256, according to Mindat mindat.org/min-1052.html Jan 9 at 19:52
• In the far infrared, minerals can have higher indices of refraction that that. ZnSe has an index of 2.7 at 10.6 um. GaAs is 3.2. Ge has an index of 4.0. This has an important impact on lens design for CO$_2$ lasers. These are all artificial substances. Some are opaque in the visible. Jan 12 at 22:20
• @mmesser314 Well, while that is useful, Im more asking in terms of visible light Jan 13 at 3:43