Key: pun

I nearly lost my marbles when I learnt that Obsidian isn't a rock. Rocks are by definition made up of minerals, which in turn are crystalline by definition. Of Quartz, Obsidian is not crystalline and is classified as an igneous GLASS rather than a rock.

Granite, I felt so stupid when I found that out. Its jet so surprising.

Well schist, its slate, its been gneiss but I better get to bed. I'll chalk up some more facts later.