http://b4hntuy3fimfh2227vf4f74emnya7p35i5brtqujs6leqvtclfwvjbqd.onion/doc/physics/diamonds-crookes/The%20Project%20Gutenberg%20eBook%20of%20Diamonds,%20by%20William%20Crookes..html
Professor Maskelyne considers it
to be a hydrated bronzite with a little
serpentine. The Kimberley mine is filled for the first
70 or 80 feet with what is called “yellow
ground,” and below that with “blue ground”
( Fig. 4 ).