#MinCup24 proustite vs titanite

It is a truth universally acknowledged that a good refractive index is a prerequisite for making a mineral sparkle.

Today's rivals both have splendid RIs: titanite up to 2.1 & proustite up to an insane 3.1 (even diamond only manages 2.42).

But alas! Proustite is light-sensitive, so needs to be kept in the dark. Here's a quick peek at one of the worlds best specimens, bought in 1876 for £200 by Henry Ludlam & now in the NHM. More in Alt txt. @MineralCup