How Gold Reacts In Black Sand

[cecc]

Just saw this interesting video on how gold reacts in black sand. Enjoy.

[video=480,360]https://www.youtube.com/watch?v=PbQA_tfC1vQ[/video]

 

[blennus]

My suspicion would be that the black sand forms a "floor" on the bottom of the pan... the black sand at the top makes way because there is more space for the sand and the gold to move around in... when you get to the bottom the black sand can't move down any further and therefore less room for it to wiggle and make space for the gold to drop through?