http://b4hntuy3fimfh2227vf4f74emnya7p35i5brtqujs6leqvtclfwvjbqd.onion/doc/physics/diamonds-crookes/The%20Project%20Gutenberg%20eBook%20of%20Diamonds,%20by%20William%20Crookes..html
Here, amidst such whirls of dust as
are nowhere else seen, the marl stuff is
pounded, sifted from the finest powder of
lime and clay, and from the residue put
on the sorting-tables, the diggers, with a
piece of zinc 9 inches long by 4 inches in
breadth, search out in the successive layers
taken from the heap the precious gems.