c/geology-rocks

My buddy insisted you can't get decent agates within 50 miles of a city, but I found a killer one right outside the Portland city limits.

He said all the good spots get picked clean, but after 3 trips to the same gravel bar on the Sandy River, I pulled out a 2-inch moss agate with perfect banding.

Rant: I used to think you had to clean every rock you found in the field

For years, I'd bring back samples from places like the Black Hills and scrub them with a toothbrush and mild acid, thinking that was the 'right' way. I changed my mind last fall after a trip to a shale outcrop near my home. Cleaning a piece removed all the tiny fossil fragments that made it special, turning it into just a plain gray rock. Now I only clean stuff if the dirt is hiding key features, and even then I'm super careful. How do you all decide what to clean and what to leave alone?

My rock hammer hit 500 hours of field use and I'm weirdly proud

Some guys think a tool is just a tool, but I logged every trip. It's seen the whole Mojave, from granite to basalt. When do you consider a piece of gear truly 'broken in'?

Tried vinegar on a weird rock from the creek and it totally fizzed

Honestly, I was just messing around with some stuff I found in the creek behind my place. I had this one lumpy, kinda yellowish rock that felt really light. I remembered something about using vinegar to test for calcite, so I grabbed the plain white vinegar from my kitchen. I put a few drops right on it and it started fizzing like crazy, like a soda. I wasn't expecting that much of a reaction at all. It went on for a good 30 seconds. I looked it up and learned that it means the rock has carbonate minerals in it, which makes sense for the area. Now I keep a little bottle of vinegar in my field kit just for quick tests. Has anyone else had a rock react way more than you thought it would? What did you find out it was?

Question about cleaning a really stubborn fossil

I was trying to clean this crinoid fossil from a creek bed near Lexington, and it was just caked in this orange iron oxide crust. I tried a dental pick for hours and got nowhere. Out of pure frustration, I grabbed some white vinegar from the kitchen and let it soak overnight. Woke up, rinsed it off, and the crust just flaked right off with a soft brush. I know acid can damage stuff, but a 5% vinegar soak for 12 hours was the perfect trick for this specific gunk. Has anyone else used a weird household item on a fossil that actually worked?

Wasted $200 on a 'rare' geode that was just a painted river rock

I bought it at a roadside stand in Sedona last year, convinced by the seller's story about it being from a secret volcanic vein. Got it home, cracked it open with my rock hammer, and found nothing but solid, gray concrete inside. The 'crystals' on the outside were just glitter glue. I should have checked the weight and done a simple scratch test first. Anyone know a reliable way to spot obvious fakes like that before buying?

That time in Moab when I learned the hard way about desert rock

I was out near the Slickrock Trail about two years back, just grabbing a cool looking red sandstone sample. I mean, it was a small piece, maybe the size of my hand. I put it in my pack and forgot about it until I got back to my tent that night. The thing had basically turned to sand and grit, ruining my water filter and getting into everything. I had to buy a new filter for like 80 bucks the next day in town. Now I'm super careful about what rocks I collect and how I pack them, especially in dry places. Has anyone else had a rock just completely disintegrate on them?

Just hit 500 hours logged on my rock tumbler and I'm honestly shocked

I bought this cheap Lortone 33B three years ago for a small project. I started keeping a log just to track grit changes and water levels. Honestly, I opened the notebook today and the total was 512 hours. That's like 21 straight days of this thing running in my garage. I guess I got way more into polishing agates from Lake Superior than I thought. Anyone else ever add up their machine time and get a weird reality check?

A quick vinegar test on a 'petrified wood' piece from Arizona went badly wrong

I bought a nice looking specimen at a shop in Sedona last month, labeled as petrified wood. I wanted to check for calcite, so I put a single drop of white vinegar on a small corner. It didn't just fizz a little, it started a fast reaction and left a permanent white crust spot about the size of a dime. I think the piece might have been treated with a sealant or something. Has anyone else had a simple test ruin a sample because of an unknown coating?

Bought a 'rare' thunder egg online for $75 and it was just a painted river rock

I saw this listing from a seller in Tucson that said it was a genuine Oregon thunder egg with agate inside... but when it arrived, you could see the paint flaking off the outside. I tried to cut it open with my tile saw and it was just plain gray stone all the way through. Has anyone else gotten burned by a fake mineral listing, and how can you tell the real ones?

I've been calling it 'fool's gold' for years, but a kid at the rock show last weekend corrected me and I feel dumb lol

I volunteer at our town's annual gem and mineral show, and I was showing a bunch of pyrite samples to a group. I kept saying 'and this shiny one is called fool's gold.' This 10-year-old kid just looks at me and goes, 'My book says it's iron sulfide.' He was totally right, I was just using the nickname like it was the real thing. It's pyrite or iron sulfide, not fool's gold. That's just what people call it when they don't know better. Kinda ironic, huh? Has anyone else had a basic geology term they realized they've been saying wrong forever?

PSA: My old geology professor's trick for finding garnets in Vermont schist actually worked.

I was out near Rutland last fall, just hitting schist with my hammer and not seeing much. He always said to look for the specific rusty orange stains on the rock face, not just the dark spots. Found a pocket with three decent almandine crystals after twenty minutes. Anyone know other field signs for mineral pockets in metamorphic rock?

I've been calling that rock in my yard 'granite' for years, and my kid's science fair project proved me wrong

My daughter needed a rock for her 4th grade project, so I pointed to the big speckled one by the garden. She took it to school, did the scratch test with a steel nail (it left a mark), and brought home her board. Right there, in her neat handwriting, it said 'GABBRO'. I felt pretty silly. I guess I just assumed all the gray, sparkly stuff around here was granite. Has anyone else had a backyard rock totally surprise them?

Tried to clean a calcite sample with vinegar and it fizzed like crazy

Found a nice piece of calcite near a creek in Austin. Thought a quick soak in white vinegar would clean it up. The thing started bubbling and fizzing like a science fair volcano for a solid minute. Learned the hard way that acid eats calcite. Anyone know a safe way to clean that stuff without dissolving it?

I finally tried that 'rock identification by licking' thing I saw online

I mean, I always thought it was just a dumb joke, like something from a cartoon. But last week I was out near Sedona and found this weird gray rock that felt chalky. I remembered a video saying to lick it to see if it stuck to your tongue, which means it's a shale. So I did it, and it totally stuck, just for a second. It was a shale, which made sense given the area. Has anyone else actually tried this, or is it just a weird trick that sometimes works?

Just learned there's a place in New Mexico with over 300 square miles of gypsum sand dunes

I was reading about White Sands National Park and found out the whole area is basically one giant gypsum crystal field. It's not normal quartz sand, it's all gypsum that washed down from the mountains and formed these huge white dunes. Has anyone actually been there and walked on it? What's it feel like compared to a regular beach?

People keep saying a $20 rock hammer from the hardware store is fine, but my Estwing is the only reason I still have a thumb after that quartz vein in Sedona.

A park ranger in Moab told me to look for varnish on the sandstone, not just the arches.

He said the dark streaks are desert varnish, a mix of clay and manganese oxide that takes thousands of years to form, which made me start noticing the rock's history more than just its shape.

Showerthought: I thought the whole 'petrified wood is just rock' thing was a bit of a stretch...

So for years, I'd see those polished slices of petrified wood at rock shops and think, 'Okay, it looks like wood, but it's just a rock with a pattern, right?' I figured it was a neat trick of nature, but not the real deal. Then, on a trip to the Petrified Forest in Arizona, I picked up a small piece from the gift shop. The guy there told me to really look at the rings and grain under a magnifying glass. I did when I got home, and I was floored... you can see every single cell structure, the tiny pores, everything, but it's all solid quartz. It's not a cast or an impression; the actual wood got replaced, molecule by molecule, while keeping its shape. That convinced me it's not just a rock that looks like wood, it's the wood, turned to stone. Has anyone else had a moment like that where a common geology fact just didn't click until you saw the proof up close?

I finally got to see the columnar basalt at Devil's Postpile last month

Honestly, seeing those perfect hexagons up close after the hike was way cooler than any textbook picture. Has anyone else been there and know if the columns are always that uniform?

Vent: My whole weekend field trip got washed out by a freak storm in the Mojave.

We drove six hours to map a specific basalt flow, and a flash flood turned the whole access road into a river of mud. I spent two days in a motel in Barstow watching the Weather Channel instead of collecting samples. Has anyone else had a key geology trip completely ruined by weather?

My rock hammer handle split right in half on a trip to the Badlands

I was out near Wall, South Dakota last weekend trying to get a decent sample of some bentonite clay. It was my third good whack on a weathered outcrop when I heard this awful crack. The wooden handle on my Estwing just gave out completely, split lengthwise from the head down about eight inches. I've had that hammer for almost twelve years, so I guess it was just tired. I had to wrap the whole thing in a ton of duct tape from my truck just to finish the day, which was a huge pain. Now I'm stuck trying to decide if I should try to re-handle it myself or just buy a new one. Has anyone here had good luck replacing a handle on an old geology hammer, or is it usually more trouble than it's worth?

Just read that a single earthquake can move a whole mountain range over an inch

I was looking at a USGS report on the 1906 San Francisco quake and it said the ground shift was measured at 20 feet in some spots. That means the whole coastal range basically jumped that far in a minute. How does that not cause way more damage than it did?

Rant: My old rock hammer grip was a total mess

Honestly, I was out at a site near Sedona last month and another geologist straight up told me my swing looked off. He said, 'You're holding it like a regular hammer, you're gonna wreck your wrist.' Tbh, I switched to a lighter Estwing with a better grip and it made a huge difference after just a few trips. Has anyone else had to totally change their basic tool technique?

Found a weird layered rock in a creek near Boulder last month, my buddy says it's just shale but I think there's a fossil in it. What's your take?