at 660 km depth, there is a transition zone where earthquake velocities 6% take a jump…at the associated pressure of of 24 gigapascals or about 3.5 million psi… the temperature is about 1000 degrees C. the jump in velocity due to a pressure induced phase change. all of the mantle, down to the core is basically peridotite… it’s olivine mixed with small parts of sodium, calcium and traces of potassium. small parts of other iron/magnesium minerals like pyroxenes. this transition zone marks the boundary between the upper and lower mantle. Aluminous minerals, like plagioclase feldspar are first compressed…as the pressure forces atoms closer together, feldspar transforms into a garnet structure starting a 70km depth, then into a spinel structure… the coordination number of aluminum, which at the surface is 6, making for 6 bonds to adjacent atoms. the garnet structure has a coordination number of 8, allowing closer contact between atoms… silicon has a coordination number of 4…all silicate minerals at the surface consist of different arrangement of silica tetrahedra…either bound to each other or coordinated by a metal cation…in any arrangement which gives all of the basic cristal groups…at depths of 410- 660 km, silica tetrahedra begin to get squeezed together and the coordination number jumps to 6… that causes peridotite to transform into a different crystal structure that is denser-- magnesium/iron Perovskite. most of this is due to olivine, the dominant constituent of peridotite being crushed into a denser phase… On the surface of the earth, perovskite is calcium titanium oxide with a pseudocubic structure…Bridgmanite was named after Percy Bridgman who won the Nobel prize in 1946 for his pioneering work on high pressure mineralogy… it is Mg/Fe silicate like olivine is but in a closest cubic packing structure…it constitutes 93% of the earth’s mantle and is stable down to the DD" layer which is just above the core mantle boundary. pressures in the lower mantle range from 25 to 125 gigapascals at the core mantle boundary… over 3 million psi to 18 million psi…the calcium analogue of bridgmanite is Davemaoite… bridgmanite was first discovered in a meteorite that that been shocked metamorphosed into the high pressure form… it was then discovered in “ultra deep” diamonds… Davemaoite was only discovered in a deep diamond in 2021… Ringwoodite is named after the Australian petrologist, Ted Ringwood… it too is a high pressure form of olivine. It has a spinel structure… deeper than 410 to 660 km, it breaks down into bridgmanite and ferropericlase (aka magnesiowustite… or (Mg,Fe)O…Ringwood was prescient in developing his model of subduction zone volcanism resulting from the overlying shallow mantle wedge above a descending oceanic plate, being melted by fluxing of the mantle wedge by water and alkalis that originated as the plate descended. He determined this by high pressure experiments before it was confirmed by seismology and petrologic analysis.
Ultra deep diamonds that originate below the 660 km layer are still somewhat of a geologic enigma… All diamonds have to be blasted to the surface from the depths of thier origin… a slow ascent of kimberlite and related rocks that contain them would cause the diamonds to revert to graphite, as the pressure decreases… the driving force is carbon dioxide…“shallow diamonds” get their carbon and carbon dioxide pressure from recycled oceanic crust that gets hung up at the 660 km transition. Oceanic crust contains sediments and water, the former provides the carbon and both provide fluid pressure. This layer developed after the start of plate tectonics an estimated 4 billion years ago at the earliest… (the age of the earth is 4.5 billion)… some of the plates were able to sink to the core mantle boundary, but not much at the current state of earth’s evolution… ultra deep diamonds are thought to get thier carbon and carbon dioxide from primordial deep mantle… … formed when the earth accreted from the solar nebula, incorporating chondraceous material, as found in chondraceous meteorites. A couple of them serve as a reference standard for isotope systematics…this interpretation is still controversial, as the mantle has been turned over an estimated 6 times… mantle that is enriched in primordial constituents will have a neodymium 143/ Nd144 ratio that is different from mantle that has been recycled and depleted… Samarium 147 decays into Nd144 and these ratios can be plotted against each other…Ultra deep diamonds with inclusions of high pressure minerals offer a window into the deep interior earth. If I am saying anything wrong, I would very much appreciate someone else jumping in and correcting my errors… I am an amateur student, not a professional petrologist.
The deep origin diamonds could also be very ancient oceanic crust that dropped all the way down to the core mantle boundary… it’s still a matter of a lot of controversy about how much recycled oceanic crust is hung up at the 660 layer versus how much sinks thru to the core mantle boundary at the present time…you’d think that the kimberlites that bring them up could be dated using any number of radioisotopes, but the dates obtained are related to the time that the rock melted, and not the time of the layer in the mantle it originated from.
I should have said carbonaceous chondrite meteorites, rather than chondraceous ones… the proper term would be chondritic… but I meant the same thing… both contain carbon and light elements, including water and everything else needed for life- sulfur, phosphorus, potassium… and are more representative of the stardust and gas that formed our planet than metallic meteorites that came from the cores of smashed up planets early in the history of the solar system…the environment of the mantle is reducing as a whole. The crust is oxidized as a whole. ferrous iron is the reducing agent… it’s important in the abiotic creation of hydrocarbons, hydrogen and organic chemicals that lead to the development of life…the development of life on earth has been pushed back another 500 millions years, to 4 billion, at the end of the Hadean period, when the entire earth was molten and metallic iron sank into the core, taking with it siderophile elements like the platinum group of metals, gold, cobalt and nickel which explains their rarity in the crust…abiotic hydrocarbon production is still occurring today. How carbon separates out as pure substance and forms diamonds is still not understood…C02 under high pressure and temperature could be reduced to carbon, since the redox potential at high pressures and temperatures are different from what we learned in college chemistry, which pertains only to the thermodynamics of chemicals at atmospheric pressure…I’m not entirely sure about this, but I do know that C02 plays an important role in generating alkalic magmas… the most radical of which is carbonatite, which is (Ca/Na2)C03…carbonatites are the host of rare earth elements that are in short supply and are used in everything now including electronics, and super strong permanent magnets that run electric vehicles…C02 metasomatism at depth, generates kimberlites…
I’m running out to the limit of what I know and don’t want to say anything wrong… I try to fact check before I write but as an amateur and not a profession chemist, I can’t be right on most things that pertains to the deep earth… there are also areas of controversy that rage on within the scientific community… there’s not enough data and data are conflicting… rather than going out on a limb I’m going to keep my mouth shut from now on, and only talk about what is more relevant to the purpose of this forum…jewelry… .if I let geochemistry creep in, it’s by default, since the formation of gems and precious metal deposits are all geological in nature…this is a jewelry forum and not an earth sciences one… I will still be willing to answer questions on the topic but you have to realize that I am not a professional…
.thanks to all who have contributed and to all who have been and are interested… and special thanks to royjohn who has kept the discussion in perspective…
about cooking a diamond in an oven… that is not entirely true… diamond which is metastable will revert to graphite, in the presence of oxygen at 700 degrees C or 1292 degrees F, a temperature of easy flow solder, and attainable quite easily by a propane/air torch… don’t heat a diamond!
it seems that the posts are getting longer and longer; is it possible to express ideas in a shorter form? Time is money after all.
Steven,
You are on the wrong forum…the petrology/geology/meaning of life forum is to the left and down the street about 1/2 mile…LOL…just pulling your chain…just send me some of what you are smoking…LOL…actually all this stuff is pretty interesting, isn’t it? -royjohn
If your objection is purely to the length of the post (time is money) then I suggest you just skip it and move on. Twitter might be more to your taste. Some of us enjoy reading the long posts as long as they are relevant to the craft, and not just someone going off on a screed. You never know what you might learn here that could possibly come in handy, even if the information does not seem immediately relevant to you.
royjohn:
Yup, I don’t want to talk about this stuff anymore… I mentioned that this was a jewelry forum and not a rock forum…but there are a couple or three, that ask me questions that are cogent…I don’t want to go any further… fact checking each line written is a burden… I’m at my limit and don’t want to lapse into BS’ing…
Thanks for your contributions… You bring perspective to the proper care and proper way to authenticate/identify stones and its currently 99+% sufficient… but I do worry about the future as does the GIA, as I have learned for the GIA researchers who presented at the rock conference…and this stuff really is interesting because it also brings some perspective on how and why precious stones form…it’s certainly given me another perspective on them…
I wish I were smoking something else besides tobacco (bad me!) If I come across something good, I’d be happy to share it with you LOL!!!..
Again thanks… and I don’t want to go there anymore, but will answer to the best of my limits, when people ask about things like this, just because they are interested too.
Again, thanks to you and best of wishes… best of wishes to everyone who has taken the time to participate… that’s what these forums are all about and makes us a community.
my thanks to Makena and royjohn…
Makena:
your point is well taken…I don’t want to write about this anymore, but am still willing to answer specific question that those who are interest want to know about… it does take too much time, since I have to fact check every line I write for accuracy… I don’t want to just be BS’ing… please see my response to you and royjohn… PS: Makena also is the name of a famous beach on Maui…any relation to your forum username and a connection to Hawaii? If there is, Mazel Tov!.. I’m from Hawaii originally.
Sapphires -corundum - take a lot of heat not as much as diamonds, but they can be retipped with gold solder while in the setting. When using the boric acid-alcohol anti-oxidation solution, AVOID its contact with the sapphire, it will eat into the surface of the sapphire, and the sapphire will need to be re-polished. Remove any of the solution with a q-tip or paper towel dampened with alcohol. Heat the sapphire relatively slowly, then retipp, or do whatever procedure that needs high heat. If the sapphire is of high quality and possibly un-heat treated, I recommend removing it and not heating it at all. I once changed the color of a “pigeon blood” ruby when retipping, it cost me several thousands of dollars to replace the ruby. I have also pitted the surface of several sapphires by leaving the boric acid-alcohol on the surface of the sapphire. Just take your time and be careful. Btw, as I’m sure you know, never quench any too-hot gemstone, I put the stone to my cheek before dropping it into the pickle just to be sure.
That’s a lovely piece. Is it a locket?
that is loupe i was making
*** List item**
sorry empty post.
Just FYI: to you and and to all of the others who enjoyed my digression last September… a long time ago now; the annual geochemical societies’ Goldschmidt meeting is being held in Lyon, France this year, again in July. I perused the didactic sessions and there are fewer that I want to specifically attend. Unlike the last meeting in Honolulu that I thoroughly enjoyed, there are no field trips and no discount for an American Geophysical Union member. The agenda is full of advances that are technology driven. Much has happened over a year in this field, of which I’m able to understand conceptually but not quantitatively… I’m using it as an excuse to go to Europe for a month… I was once fluent in French, having lived there for 6 months and having studied French for 6 years in highschool and college, but that was a lifetime ago now. I still remember enough to travel. My travelling companion is bilingual in English and Spanish so we are also going to Spain. But this is not what I want to pass along. What I do want to pass along is the following:
I’ve been to Paris several times before. There is a small museum next to the Louvre called the museum of decorative arts. It has a permanent collection of art nouveau jewelry made by Lalique who is probably the best art nouveau jewelry maker…The collection is stunning for its exquisite craftsmanship and organic design, especially given the tools that they had available at the time… mouth blow pipes…instead of propane torches… everything was fabricated handmade. Lalique’s studio worked in mixed media, combining precious stones, enamel, glass and pearls and semiprecious gems… I’m sure that most contemporary jewelers have seen pictures of some of his creations… For anyone going to Paris, this museum should not be missed… It’s located next to the courtyard entrance to the Louvre, easy to overlook as it’s overshadowed by the huge and famous museum. For anyone who likes jewelry, this is a must see… This is what I want to pass along!!!
I don’t know how to send out a group response to those who liked my posts about geochemistry last September… I sent a reply to Neil A… if you could help me pass this along, to W,G and Y… I will be going to Lyon France for the upcoming geochemical society meeting in July… this gives me an excuse to travel in Europe again…
I want to point out that there is an exquisite collection of Lalique’s work at the Museum of Decorative Arts that is a not to be missed place to visit for any jeweler or any art historian… The museum is at the entryway to the courtyard of the Louvre and is overshadowed by it’s famous neighbor… it houses some of Lalique’s famous art nouveau pieces… the collection is stunning for its craftsmanship and difficult organic designs, given the primitive tools they had at the time, like mouth blow pipes instead of propane torches… everything was hand fabricated. Lalique’s studio worked in mixed media combining precious stones, glass, enamel, pearls and semi precious stones…This museum is a must see for any jeweler or art historian… and for the general public… It’s pretty much unknown, so I’m pointing it out in case anyone else has the good fortune to visit Paris in the future.
Bon voyage… Steve