I Guess

The Ore Leonel immediately recognized was quite a unique metal that manifested like glass. It had all the texture, feel and pliability of metal, but also happened to be see-through. This ore was simply known as Polished Glass Ore and it seemed that Kaela's faction received their name directly from this source. The only difference between it and normal glass was that it had a slight black hue to it as though in warning of its danger…

The issue with Polished Glass, though, was that it was incredibly volatile. And as Kaela mentioned, it was best not to leave it with any impurities unless one wanted a face of what would amount to a stack of TNT. 

However, as it seemed with most things, the more difficult they were to deal with, the better the reward for dealing with them. The problem, though, was that Polished Glass had a very specific use case that would benefit it the greatest and it was difficult to reach this balance.