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Rare Blue Diamonds Lurk Deep In Earth's Core (washingtonpost.com)
Scientist believe they now know how extremely rare blue diamonds are formed. After studying 46 of the gems, they found that blue diamonds are formed as deep as the transition zone between the planet's upper and lower mantle (Warning: source may be paywalled; alternative source) -- far greater depths than other diamonds, some deeper than 410 miles. The Washington Post reports: Just 1 out of 200,000 diamonds are blue. Like all diamonds, they are made when carbon comes under intense pressure and extreme heat deep inside the Earth. As they form, they can trap tiny bits of rock inside -- like fossils in amber. "Diamond is an extraordinary container, a time capsule," said Steven Shirey, a geochemist at the Carnegie Institution for Science in Washington. Shirey and his colleagues used lasers to examine the diamonds' imperfections -- slivers of embedded rock -- at the Gemological Institute of America. The researchers suggest that boron in the ocean floor was pushed down when plates that make up the Earth's crust collided. The element allows the stone to absorb some red light, so the diamond looks blue. The findings were published in the journal Nature.
TFS summary says they're formed in the mantle, not the core.
Our primal urge to mate means we need a way to differentiate yourself from the pack. One way to do this is with luxury to show that we are so successful in surviving that we can use our excess resources on things that are not necessary for survival. So there are resources available to help take care of children and expand the gene pool.
Pretty rocks, decorative flowers, larger houses... Are things we want to have, So high demand.
Then if these pretty rocks are hard to find, then we will need to compete with others to get them. so low supply.
Low Supply and High Demand = a valuable object.
Sure we use other methods, such a physique, and dominance as well. But having excess is an important factor in our species mating rituals.
If something is so important that you feel the need to post it on the internet... It probably isn't that important.