Rant: A simple granite slab identification turned into a three day puzzle

A client in Phoenix wanted to know if their kitchen counter was 'real' granite or a lookalike. I told them to do the scratch test with a key, expecting a quick answer. The key left a mark, which should mean it's softer than quartz, but then the acid test didn't react at all. I spent the next two days digging through old geology texts and calling a buddy who works in a quarry before we figured out it was a specific, dense gneiss that polishes up like granite but has different properties. Has anyone else had a common test totally backfire on them?

3 comments

3 Comments

spencerh952mo ago

Ever have a project that should take five minutes and then eats your whole week? That scratch test is such a classic trap. It feels like a sure thing until the material decides to break all the rules. Sounds like you ran into the rock world's version of a glitch in the matrix. At least you got a good story out of it, even if it cost you three days.

miles_campbell392mo ago

Always run a second test on a fresh spot, just in case the sample's got a weird vein or something.

beth_green21d ago

You're spot on with the "glitch in the matrix" thing. I had a similar head-scratcher with a quartzite once that would not scratch at all, but a drop of vinegar left a dull spot after a few minutes. Turned out it was a very fine-grained marble that had been heated and compressed, fooling everyone. What finally worked for me was checking the bottom for any raw, unpolished spots and testing there instead of the surface finish.