So diamonds are compressed coal, is that right? Are there examples in existence of coal in the process of being compressed into diamonds but it hasn’t finished yet?
Diamonds were formed on earth a long time ago.
Here is a quote from Wiki…“Most natural diamonds have ages between 1 billion and 3.5 billion years. Most were formed at depths between 150 and 250 kilometres (93 and 155 mi) in the Earth’s mantle, although a few have come from as deep as 800 kilometres (500 mi). Under high pressure and temperature, carbon-containing fluids dissolved minerals and replaced them with diamonds. Much more recently (tens to hundreds of million years ago), they were carried to the surface in volcanic eruptions and deposited in igneous rocks known as kimberlites and lamproites.”
The same Wiki article suggests that diamonds may be abundant in places other than Earth. Future advances in space exploration may totally destroy the lucrative diamond market!
I don’t see how that precludes new diamonds from being formed now - maybe in subduction zones, for example, where rocks containing carbon in non-diamond form may be fed into the mantle. Obviously we’d never be able to get at those diamonds anytime soon, if they are being formed there.
Although diamonds are made of carbon, AIUI they are not simply compressed coal. The descriptions in this thread of the diamond formation process indicate that carbon-bearing fluids are the the most proximate source of carbon. It may well be that the carbon in these fluids was previously present in a coal formation a long time prior, but despite what you may have seen, I think geologists would not support the claim that diamonds are compressed coal.
When diamonds formed >1 billion years ago, there was no coal.
The diamonds from coal idea seem to have been around forever, I’m sure I was told this when I was in primary school. Then again, it wasn’t just Superman the movie, there was an original 50’s b&w Superman TV episode where he crushed a lump of coal in his hand to make a diamond. So I guess it must be true.
In reality, even at the depths that coal occurs, the pressures are much too low to convert it to diamond.
Carbon is the fourth most abundant element in our galaxy; I think people probably assume coal is the origin of diamonds just because coal or charcoal are the most common everyday ways that people have been encountering carbon as a recognisable material, for a long time.
(sure, graphite in pencils is also common, but we’ve been busy calling that ‘lead’)
No, that’s not right, like everyone else has said.
It’s a myth to think diamonds are compressed anything. They crystallised out of a hot fluid. And the most likely source of their carbon was inorganic carbonate rocks of the early Earth, or primordial carbon that was in the mantle from formation.
Diamonds are just a form of carbon, but, oddly now that I think about it, this is a very interesting question. Picture a carbon cycle - but I’m talking about the element here. It gets bounced around in rocks and biological systems and what not… but if it crystallizes into a diamond, that’s pretty freaking stable. It breaks the cycle. That carbon atom doesn’t cycle through anymore. Now, there is plenty of carbon of Earth, so it’s not like biological life is ever going to run out of the stuff, but it is kinda interesting to note that there is a “sink” in the carbon cycle, and it’s diamonds.
You haven’t broken the cycle, since diamonds are unstable at atmospheric pressure and will spontaneously un-form and turn to graphite.
Diamonds do not become graphite. Just… no. Diamonds are not unstable at atmospheric pressure. Nobody’s engagement ring is going to turn into pencil lead. Simply put, just no.
Diamond is metastable at STP, there’s not a lot of spontaneous decomposition happening. At normal surface conditions, diamond will last.
Of course, nothing on the Earth’s surface stays at STP for all that long.
It is an artificial market, it deliberately keeps supply tight. It has survived lab made diamonds which are diamonds. So the scummy diamond industry is probably pretty safe from space diamonds.
Which, oddly, gets back to my idle observation about geological carbon. If we assume that the supply is finite, then, well, there is a non zero loss of usable carbon to diamonds due to geological processes. It sure as hell isn’t significant, but it is non-zero.
So as to the OP: The Planet Earth will always form diamonds, all it needs is carbon, which is plentiful. Not just in coal, or biological systems. the element is everywhere.
You’d have to balance it against the incoming carbon in carbonaceous meteors before you can say if there’s a loss or gain…
So I don’t see anything or anyone contradicting this idea?
It takes (or took) a billion+ years for diamonds to migrate to the surface from where they form(ed). I don’t see what has changed so that diamonds would no longer form. Although maybe their migration to the surface has slowed or stopped (less geological activity).
So can one confidently state that diamonds are still forming in the earth’s mantle?
It’s a large planet. I think we can safely assume that there are places where diamonds are in the process of being created. As mentioned, they are much more plentiful than many people believe because the Diamond Cartel manipulates prices by controlling the diamonds released for sale. It used to be solely De Beers that controlled the market, but now it is a group.
A very interesting article:
That is a good, succinct Power Point display on the issue. Quick read, covering enough details.
Not exactly. The emplacement was more-or-less instantaneous in geological time.
Kimberlite eruptions were powerful. Supersonic explosion-powerful
Not likely. If they were still forming, we’d see them in kimberlites. But the gap in age between the youngest diamonds in kimberlites and the actual kimberlites themselves is big enough - hundreds of millions of years - that it seems like *something *stopped mantle diamond formation (or at least - *that *kind of diamond formation. microdiamonds and the like *are *still being formed). Possibly a change in the mantle heat flow or similar.