Scratch test solved my basalt vs coal confusion

Honestly, I found this smooth, dark rock in a dry riverbed. Tbh, I couldn't tell if it was basalt or something else. Ngl, I tried scratching it with a knife and it left a mark. I looked up hardness scales and compared it to my samples. Finally, I realized it was anthracite coal because it was lightweight and left a streak. Now I always carry a streak plate with me. Anyone have tips for field identification?

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3 Comments

loganrobinson7mo ago

What kind of knife were you using for the scratch test? I've had different results with a cheap pocket knife versus a steel file. Also, ever use the back of a ceramic tile from a hardware store as a streak plate instead of carrying an actual one?

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seanh917mo ago

Actually, why would you want consistent scratch results anyway? Different tools telling different stories seems more useful. And carrying a real streak plate takes zero effort, so why bother with tile scraps?

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nora_scott867mo ago

Yeah that confusion is so real, I've totally been there staring at a dark rock for way too long. I get what @seanh91 is saying about different tools giving different info, but for me, I need that one reliable scratch test to even start figuring it out, you know? Otherwise my brain just spins in circles. The streak plate thing is a game changer, even a broken piece of ceramic from an old mug works in a pinch. It just makes the whole process less of a guess.

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