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  • Carbonados, sometimes referred to as black diamonds, have been on geologists' radar

  • since their discovery in 1841.

  • They look neat, and have some cool industrial uses.

  • But there's a lot we don't understand about this particular flavor of sparkly rock.

  • Like where on Earth they come from.

  • ...If they come from Earth at all.

  • As you might expect, carbonados are black.

  • Or at least, they're dark.

  • They're opaque, and really can range anywhere from grey to pink to green.

  • And they're sometimes used in jewelry.

  • But because carbonados are rarer than diamonds, much of the black diamond jewelry on the market

  • is made from naturally occurring diamonds with darker colors, or ones that have been

  • treated to change their color.

  • On the other hand, carbonados, though made of diamond, are a little different from the

  • one you might be picturing.

  • They're crystallized carbon, so they still fall into the diamond family, but instead

  • of tight, continuous, uniform crystals like most diamonds, they're aggregates of a bunch

  • of randomly arranged microcrystals.

  • This arrangement makes carbonados something geologists refer to as a xenomorph.

  • In part, this means that carbonados are more porous than single-crystal diamonds.

  • But this weirdone might even say Aliencrystal structure also makes carbonados

  • extra useful for industrial purposes.

  • Diamonds are really hard, and we like to take advantage of that fact by using them for cutting and drilling.

  • But even diamonds can eventually crack or break, and then you have to replace the cutting

  • surface with new diamonds.

  • However, carbonados have an advantage.

  • Since they're aggregates, rather than uniform crystals, any break will be confined to that

  • single piece, and not spread throughout.

  • This makes carbonados as hard as diamonds, but much tougher.

  • Hardness is a material's ability to withstand abrasion, and here, carbonados match your typical diamond.

  • Toughness, on the other hand, is how well a material resists shattering when force is

  • applied, and that's where carbonados come out on top.

  • Thus, they allow cutting and drilling tools to last longer and require less maintenance over time.

  • But the main reason scientists are interested in carbonados isn't what they look like

  • or even what they can doit's their origin.

  • And the origin iswe don't know.

  • The majority of ordinary diamonds form in the intense heat and pressure of the Earth's

  • mantle, before eventually being blasted to the surface by volcanoes, and encased in rocks

  • with characteristic mantle minerals.

  • But that doesn't seem to be the case with carbonados.

  • They're not found in mantle rocks, and tend to include metals in their structure that

  • wouldn't make sense if they formed in the mantle.

  • Theories for how carbonados form include the heat and pressure of meteorite impacts, or

  • possibly even radiation transforming carbon in the mantle.

  • However, neither method produces diamonds large or numerous enough to account for existing carbonados.

  • Another contender is subduction zones, boundaries where tectonic plates collide and get shoved

  • down into the mantle.

  • The pressure and heat of this process would be plenty sufficient, but again, we should

  • find mantle minerals present alongside carbonados.

  • All this leads scientists to suspect that carbonados must come from interstellar space.

  • The crystals could form out there in some distant, carbon-rich spot, in the absence

  • of Earth mantle minerals, and then get deposited here via asteroid.

  • Plus, the space option could easily account for those head-scratching metal inclusions.

  • Furthermore, carbonados are only found in Brazil and the Central African Republic, which

  • could be explained by an intense barrage of space rocks back when Africa and South America

  • were part of the same supercontinent.

  • All of this makes carbonados one of the few geological phenomena where the most likely

  • explanation invokes outer space.

  • Because once you've eliminated the impossiblewell, you know.

  • Thanks for watching this episode of SciShow.

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  • [ ♪OUTRO ]

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B1 mantle diamond jewelry cutting carbon black

The Mystery of the Black Diamond

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    林宜悉 posted on 2020/03/30
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