Vent: My vinegar test on a rock from Lake Superior backfired

I picked up this grayish rock near Marquette, Michigan thinking it might be limestone. When I put a drop of white vinegar on it, there was zero fizz, but the spot turned a weird orange color overnight. Turns out it's a piece of banded iron formation, and the acid reacted with the iron oxides. Anyone know a better way to test for iron content without messing up the sample?

2 comments

2 Comments

barbara_kim11d ago

The vinegar test actually worked, it just gave a different result than you expected. The color change is a positive reaction for iron. A small magnet is a safer, non-destructive way to check for iron minerals.

miller.eva11d ago

My buddy Jake tried the vinegar test on a rock last month. He got that orange color and thought it was a dud, but his geology professor said it just meant high iron content.