230
And Quartz, of course
(imgs.xkcd.com)
Source: https://xkcd.com/2501/
Alt text: "How could anyone consider themselves a well-rounded adult without a basic understanding of silicate geochemistry? Silicates are everywhere! It's hard to throw a rock without throwing one!"
You know, you might just be on to something. He sure didn't seem like he was particularly into it.