My brother-in-law said 'obsidian isn't a real rock' and it got me thinking

We were looking at a piece I found near Mount St. Helens last fall, and he said because it's volcanic glass and not crystalline, it doesn't count. He's a chemist, so he was really firm on the 'mineral structure' thing. But that feels wrong to me. If it comes from the earth and is solid, it's a rock. I've been reading up and it seems like even geologists argue about this. Has anyone else had a debate about what actually makes a rock a rock?

3 comments

3 Comments

kim8191mo agoMost Upvoted

Chemists need to chill. It's a rock.

abby9261mo ago

But what's the real problem here? Is it about being technically right or just wanting to win an argument? The definitions are pretty clear if he'd actually look.

adam_adams1mo ago

Your brother in law is technically right about the mineral part, but he's missing the bigger picture. Rocks are just solid natural stuff from the earth, and obsidian fits that bill perfectly. Geologists call it a rock all the time, even in textbooks. Tell him to check the definition of 'rock' versus 'mineral' and get back to you.