One of my absolute favorite parts about teaching geology is when people bring me mystery rocks/minerals to identify. Not only do I love rocks, but this shows me that others care about what I do, even if they don’t have a lot of experience with geology. Sometimes these are students from my classes, but occasionally other faculty members or even people from the community will stop by looking for answers. I have noticed, as perhaps many of you have as well, that MOST of these rocks are fairly common. Ok, I guess “most” of anything is by definition “common”, but that’s beside the point. I’m just saying that these found specimens are rarely Archaean komatiites or hunks of primitive mantle. To save time, I’ve developed a foolproof system that promises to help you to identify virtually all of these mystery rocks/minerals without ever actually looking at them.

The Super Foolproof Volcanoclast Guide to Identifying Almost Every Mystery Rock/Mineral Without Ever Actually Looking at them.

Step 1: Tell them it’s quartz. I don’t care what it looks like or where they found it. Tell them it’s quartz and you will be right 95%* of the time. Is it white? Quartz. Is it light gray? Quartz. Is it milky colored? Quartz. Do they think it’s a diamond? Quartz. We could probably stop right here and call this the It’s-Always-Quartz-No-Matter-What-Guide.

Step 2: If they think it’s a meteorite, it’s slag (byproduct of iron smelting). Again, you don’t have to look at it to be 98% sure. There’s a reason most meteorites are found in Antarctica and not in a pile of other rocks. In northeastern PA, where I work, I get at least one piece of slag a year and people are SOOOOOOO disappointed when I give them the bad news. Next time, I’m telling them it’s Kryptonite. Once in a lifetime it might actually be a meteorite, in which case you simply tell them it’s slag and that you’d be happy to dispose of it for them.

Step 3: If they think it’s gold, it’s pyrite (obviously). Now this seems like a no brainer seeing as pyrite is also known as fools gold, but you’d be surprised how often people fight you on this. If they don’t believe you, suggest they try to bite it in half, then watch in horror as they actually try to do it. PLEASE DON’T EVER BITE ANY ROCK OR MINERAL ESPECIALLY IF YOU THINK IT’S GOLD. IT ISN’T. IT WILL BREAK YOUR TEETH!!!

Step 4: They say they found a gray rock in a river. In this case, give them a detailed explanation of the importance of texture in identifying rocks and how rivers tend to wear away this helpful information, so there really are a number of things it could be and it’s a little difficult to say for sure without doing more testing, but if they really want to know, you could borrow the rock and get back to them and with any luck, they stopped listening several minutes ago or even fell asleep at which point you can make your escape. The key is to never EVER admit that you don’t know what it is under any circumstances. Its a good lesson for the kids.

Step 5: They say they found a fossil. This one is easy. Pterodactyl. Always Pterodactyl. If they aren’t buying it, just say it’s a plant fragment, which, let’s face it, 99.9% of all fossils are.

Step 6: It’s got a bunch of different “stuff” in it. Now, you geologists out there are screaming “it’s conglomerate!” and maybe it is, but it’s just as likely to be a broken piece of urbanite (that’s concrete for those who didn’t get my clever joke). Concrete is often mistaken for conglomerate and for good reason. They’re both made of poorly sorted sediment, cemented together into solid pieces that are resistant to weathering. Its still fun to watch students debate the depositional environment of a piece of concrete, mostly because that used to be me.

Step 7: They think it’s amber. It’s not. It’s glass. Now this one, I have a little experience with. I got a a call from someone claiming to have “found” a 30 pound piece of amber, which would make it perhaps the largest piece of amber ever “found”. I asked where they “found” it and they answered “New Jersey”, otherwise known as the “Amber Capital of the World”. This person clearly needed to be let down easy, so I agreed to take a look at what turned out to be a giant hunk of broken glass. I tried to get more info on its provenance, but they were cagey on the details. Sometimes, it’s best not to pry.

So, there you have it. A foolproof guide to identifying virtually any mystery rock someone might throw at you (The mystery is being thrown, not the rock). If you do happen to have an Archaen komatiite, stop on by and let’s take a look. Just don’t be surprised if I say it’s quartz.

* I plan on making up these percentages for the duration of the post, so please don’t try adding them up. They will not add up to 100%. I promise.