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The reason minerals like quarts and diamonds vary in color is generally caused by the chemical elements involved while the crystal is being formed.
Chemicals
Different colors can be created by different chemicals. Amethyst for example has traces of iron built into its crystalline structure giving it a purple hue. Iron can also give crystals a yellow hue.
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It is bond strength, not hardness, that determines how easily oxygen
can attack and burn a material, allowing me to burn a diamond in a
pool of liquid oxygen resting in a block of graphite.
Diamond is hard because its bonds form an inflexible, three-dimensional lattice. However, the strength of these bonds themselves is not even as strong as graphite, ...
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I would think this is questionable, though we don't have a definitive answer yet.
We usually think Jupiter has a roughly solar composition, which according to the solar abundance measurments of Asplund et al. 2009 would mean the total carbon mass of Jupiter is about $10^{-3}$ of Jupiter's total mass. So there's roughly $0.3$ Earth masses of carbon floating ...
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I'd like to elaborate of the Chemicals issue of Azzie Rogers' answer.
You can divide the chemical coloring into three main parts (there may be more, but these are the important ones):
Inclusions
A large, solid crystal can have tiny inclusions of other solid minerals. Commonly these inclusions are too small to individually observe by the naked eye. ...
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Diamonds are expensive. Really expensive. Even "cheap" synthetic diamonds are orders of magnitude more expensive than conventional fossil fuel. By using them as fuel, you will increase demand, thus increasing their price even more. And synthetic diamonds have to be made somehow, and you need energy for that.
Diamonds burn, but they don't burn well. For ...
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Craters actually can be identified by formation of high-pressure materials such as diamonds or stishovites and coesites (varieties of shocked quartz). A good example of this is the Popigai crater in Russia.
Pressures and temperatures at subduction zones are usually too low to form big diamonds but microdiamonds (10-80 microns) were discovered within ...
7
The main hard rock sources of diamonds are either kimberlites or lamproites.
Many kimberlite and lamproite deposits occur as:
carrot-shaped, vertical intrusions termed 'pipes'
As the term "carrot-shaped" suggests, the general shape of the pipes is conical and when viewed in horizontal cross-sections they are generally quasi-circular.
When such ...
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Diamond isn't made of organic C at all. Organic matter would rather become oil, gas, coal or dissolve entirely.
C itself isn't very common in earth's mantle, but subducted eclogites and peridotites can lead to the needed C-accumulation.
But also meteorite impacts can lead to the genesis of so called micro-diamonds due to the very short lasting but extreme ...
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Not so fast, we can't say that 'no diamond is made of organic carbon'. There are two types of diamond, based upon the relative abundance of $^{12}C$ and $^{13}C$ isotopes. The 'lighter' carbon (relatively $^{13}C$ depleted) are thought to arise from crustal carbon-bearing rocks, possibly including some organic carbon, that was subducted into the mantle, ...
5
Impact diamonds
Yes, diamonds can form in meteorite impacts. For this several things need to happen:
A meteorite of the correct size and velocity,
The stuff it hits needs to contain carbon.
If you have a meteorite hitting granite or ocean you're not going to get any diamonds. It usually has to hit something that has biogenic carbon (let's say peat, coal, ...
4
what is stopping someone from building a high-pressure, high-temperature system and dumping graphite in and making millions of diamonds?
What is stopping someone from making these HPHT machines and making tons of money?
No one, and it is done. First of all, synthetic diamonds have been out on the market for quite some time now and it's a well ...
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Sapphires and ruby's are both aluminium oxide. sapphire melts at 2000 degrees and diamond synthesis can happen at 600 degrees. To coat around the sapphire, you would have to use multiple diamond seeds, which would make a polycrystal. it's probably humanly acheivable.
The scientists would have to study the adhesion of a transition layer, because the ...
3
But did plants and trees of 300 million years ago sink so deep?
300 million years ago (Carboniferous) was a time when large amount of organic carbon was buried to a depth of several kilometres and formed large beds of coal. The pressure and temperature was only moderate (which is why you have coal and not diamonds).
Diamonds form at depths of hundreds of ...
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Nowadays impact craters are of little significance. Back in the Hadean era of early planetary crust formation, bolide impacts were the defining process of planetary evolution.
As for diamonds, one might expect micro-diamonds to be formed in rare instances of carbon-rich impact craters. On the other hand, back in the days of early lunar exploration, some ...
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To make it even more difficult, recent research revealed existence of microdiamonds. Tiny diamonds (microscopic) were discovered inside kyanite or garnet within granulite rocks. So our explanation for diamond formation is at least partially wrong (they form at much lower pressure then anticipated) or we have some problems with understanding of granulites and ...
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Scarcity is the biggest limit, diamonds burn much like coal but unlike coal they are extremely rare.
artificial diamonds would still cost vastly more to make than digging up coal.
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It's worth noting that our planet was formed by "meteorite" impacts and that our own moon is the (geologically important) result of Mars smacking into our planet, but let's focus on impacts after, say, the Archaen.
If we lived on the moon, impact craters would pretty important to our geology. As it is, it's perhaps a lot more important to our biology than ...
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