TIL I'm not as good at spotting different rocks as I thought.

I went hiking over the weekend and was sure I found a bunch of quartz, but when I got home and looked closer, half of it was actually calcite. I guess I was just seeing white crystals and getting excited. I tried the scratch test with a penny, and that's when I figured it out. It's a bit of a letdown, but now I want to get better at telling them apart on the spot. Does anyone have a simple trick they use in the field to tell quartz from calcite without carrying a whole kit? I really want to avoid filling my pack with the wrong rocks next time.

3 comments

3 Comments

aaron_flores841mo ago

Yeah, a pocket knife blade works for that scratch test too.

faith1091mo ago

My buddy got super excited about some "quartz" he found last year and filled his whole pack with it. He was using a pocket knife like @aaron_flores84 said, but it turned out he was testing on a weathered surface. Every piece scratched. He brought it all back and it was just soft calcite that had crusted over. The knife trick works great, but you gotta make sure you're testing a fresh spot. That mistake taught him to always find a clean edge before trusting the scratch.

quinnb361mo ago

Hold up, you tried the scratch test with a penny? That's actually pretty smart for a quick check! Quartz is way harder than calcite, so it should scratch glass easily. Calcite will scratch with a copper penny though, which is why it worked. For the field, just carry a small piece of glass or a steel nail to test hardness. That way you don't end up with a bag full of calcite again, lol.