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A local rockhound told me my 'granite' find was actually just a big chunk of weathered concrete.
I was showing off a piece I found near the old rail yard, and he pointed out the aggregate and lack of crystal structure, so now I always check for air bubbles and do a basic hardness test before getting too excited.
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kevin_lane7mo ago
What hardness test do you use?
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burns.fiona7mo ago
Honestly it depends on the part geometry more than the material sometimes. I've had to use micro Vickers on tiny, thin sections where a Rockwell indenter would just go right through. The prep is a pain but it's the only way to get a real reading on something like a razor blade edge.
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spencerross7mo ago
My buddy learned the hard way that the Rockwell C scale is the only one that matters for his tools. He tried using Brinell on some alloy steel and got numbers that made no sense at all. The shop foreman chewed him out for wasting half a day on a test that wasn't right for the material. Now he double checks the spec sheet every single time before he even touches the tester. It saved him from a lot of pointless extra work.
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shane_morgan5mo ago
Wait, do you mean for just rocks or are you asking about general hardness testing? @burns.fiona makes a good point about sample size mattering more than people think, and I'd bet most folks checking concrete chunks aren't thinking about micro Vickers at all. Curious if you've tried the simple scratch test with a steel nail on your finds before jumping to the more serious gear.
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