This is really an excellent thread
There was an occurrence of a substance being mistaken for fools gold (calverite)
Well it turns out that calverite hides gold within.
Here’s the blurb form wiki
“In the Kalgoorlie gold rush of the 1890s, large amounts of calaverite were mistaken for fool's gold, and were discarded. The mineral deposits were used as a building material, and for the filling of potholes and ruts. Several years later, the nature of the mineral was identified, leading to a minor gold rush to excavate the streets.”
Its a hilarious story. Cause miners were discarding these rocks while getting to the gold. They used these rocks to build their houses, roads ect… A few years later a chemist discovered the truth about these discarded rocks.
Hence the second gold rush