Here are some pieces of relevant infomation to further the
discussion. I would recommend some googling and examining of
pictures online as well as text.
(1) The Audubon Field Guide gives an SG range of 3.1 to 3.5 for the
various forms of C allotrope diamond in the field which is > 10%.
(2) Yes, I agree with you and Nick about the role of pockets,
cracks/faults and chemicals mixed in with C which may alter colour
and SG greatly especially given that some diamonds are found in rock
thought to have formed 3 bya and there is enormous TIME for these
changes to happen to the original C. So we ask about the history of
C over billions of years.
(3) In addition to googling add the Harvard material there is a
series of Princeton reports with quotes like “The role of water in
the growth of carbonado awaits further explanation” and “in contrast
to kimberlite diamonds, the geochemical signature of carbonados are
systematically crustal”. I think the word “GROWTH” is important in
contrast to the flash formation of diamonds in meteorites etc.
including the Discovery TV demo of backyard explosions to produce
diamonds (which everyone should rush out to try in yard or basement
or apartment balcony of course).
(4) Dispersion of the fluids which were discussed and demonstrated
empirically in the Harvard material may be impacted by quantum
effects as we read in Physics Today of August 11/10 “Quantum Effects
Turn Pore Diffusion on its Head” and in particular Zero Point Energy
may cause molecules to disperse to different degrees and “by a
substantial margin” with H2 and D2 used in the experiments.