Does anyone on Orchid have experience with the diamond anvil? If
nephrite has a more “cohesive” crystal structure (Bloss, page 354)
would it be better to use nephrite which also would allow larger and
cheaper anvils to be built?
Diamond anvils are used in ultra high pressure triaxial testing of
(typically) single crystals. They consist of 2 optically perfect
diamonds opposite each other in a press with a confining ring of
metal and are fluid filled (normally liquefied noble gas) to provide
the confing pressure. Diamonds are used because they are optically
transparent, cubic-so you do not get interference colours under
polarised light and transparent to infra-red radiation and have a
low atomic number (LZ) so as to be x-ray transparent. They are
incredibly tough and do not exhibit creep under these conditions.
Other materials can be used for UHP optical studies such as CZ or
moissanite but these materials are not suited X-ray work
Nephrite does not fulfill any of these criteria.
Best regards,
Nick Royall
I have been reading Bloss, Wahstrom et al and trying to learn some
crystallography, especialliy at a microscopic or barely visible
level.
For example, what if you are prospecting and find barely visible
crystals in an ore body which is 40% or more olivine with pyroxene in
the second spot and they flash a lot of light at noon-day sun? IMO it
is reasonable to find out if they are diamonds.
Would a diamond anvil tell you? Otherwise what is the lowest cost
method for diamond determination at this size?
Wahlstrom of course refers to the polarizing microscope for “thin
slices” but what about tiny crystals as above? What do you think the
De Beers Lab at U Alberta uses?
PS - Would wurtzite boron nitride be a stronger material to
substitute in a diamond anvil? As we determined in that thread last
year, ALL crystals will pass light if small/thin enough. So if lasers
can penetrate the WBN, the laser-temperature tests can be done though
maybe WBN is not as heat-resistant as diamond.
Bloss gives 5 main parameters plus sub-parameters for crystal
"COHESIVENESS" which I expect is what you need in a diamond anvil. He
does not rank-order crystals (like diamond or nephrite) for
cohesiveness total score.
The most cost effective method of analysis is energy dispersive
x-ray microanalysis as performed in a scanning electron microscope.
If you can separate them you can also use X-ray diffraction but the
lattice spacing of carbon is very small so a bulk analysis will lose
the peaks in the low angle background noise with other minerals. The
de Beers lab will undoubtedly analyse the olivine and pyroxenes,
garnets etc and determine the geothermemetry and geobarometry by
their chemical composition. This has been the case for decades and
only if they get the right numbers will they actually bother to look
for diamonds themselves by crushing and separating a ton of rock as a
sample and assay that by centrifugally separating the correct
density material and then hand picking through it using a hi mag
binocular microscope and then some of that material will be analysed
by either x-ray microanalysis in a SEM or by diffraction in a TEM if
the crushings are very small( sub 5 micron). I used to do contract
work for them for prospects in certain countries and I never saw a
diamond. Did similar work for the Russians and had trouble doing the
sample preparation because the diamonds were so big and numerous I
couldnt cut up the rocks to make the thin sections! A polarising
microscope wont help you with your diamonds because you cant make a
thin section of them and if you could they are isotropic anyway.
A diamond anvil wont tell you anything about the composition of what
you put in it, it is a pressure vessel and these super high pressure
vessels are used to deform the lattices of single crystals for
certain purposes.
Boron nitride is not optically transparent so is on no practical use
as a diamond replacement. All materials are not transparent, just
look at metal. As I said before, diamonds are used because of the
combination of properties, not just their toughness or hardness. If
diamonds werent the most suitable material for these anvils they
would use something else instead because they are not cheap. Gold
makes a perfect non-stick frying pan but is not that cost effective.
Nick Royall
The de Beers lab will undoubtedly analyse the olivine and pyroxenes, garnets etc and determine the geothermemetry and geobarometry by their chemical composition.
Thank you for the detailed and helpful reply (which I hard copied
for my notes).
I have multi-coloured tiny crystals which I break out of the
olivine-pyroxene ore (60-80% according to highly qualified
petrographic analysis). There are hundreds-thousands in a gram and
they are very nice to look at under 20x magnification.
I am processing several tons of ore brought in from the bush last
winter to collect these samples and I had another thought about
“narrowing the odds” step by step. I can send a gram of crystals to
an assayer who does organic and inorganic C determinations.
Do you think that would help?
I gather one cannot do much with an isolated one milligram
crystal… is there a GIA scientist on Orchid who might say
otherwise?
hello, the point of the diamond anvil (no pun intended) is precision
reading when used with the correct equipment for the given
anvil/product. Nephrite wouldn’t work unless crystal clear- not to
mention that industrial diamonds, even extremely large ( relative to
the product and size of the readability) high quality ones are
readily available and plentiful- so nephrite though it may make sense
both theoretically and logically wouldn’t be accepted by the
manufacturer’s of the anvils- and a note for those of you that think
this ( a diamond anvil) is some kind of bench tool- it is not:
Rather, it is an insert into a larger piece of technically perfect
equipment for reading hardness, and tooling manufacturing purposes…
they cost in the hundreds of dollars (+$350-$1100 USD) and are
essentially useless to the studio jeweler even though they measure
hardness on a Rockwell scale, but primarily used in manufacturing
steel tooling and precision set-up of complex tooling equipment. If
anyone however needs one I have a very specific size v point anvil
(new) for sale if you want to play around with it at a fraction of
the original price- I purchased the wrong size inadvertently and the
vendor specified no refunds on this type of product as its use was
beyond the control of the vendor- so I’m stuck with a very expensive
thing I can’t ever use…In fact this is the first time in years and
years of my membership in ganoksin that I am hearing of anyone even
discussing the part!..I will be happy to provide the tech specs to
potential serious buyers if necessary… rer