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I once ran across a question on this forum a few years back that questioned if mountains made out of diamond could reasonably exist. Ever since then I've been interested in the concept of diamond mountains on my planet and I designated a random desert, the Yyn desert which I had previously not written about as my diamond desert. The idea that I had at that time, and that I still hold for now, is that a series of short mountains in the middle of the desert over time eroded away into this desert of small diamond partials.

Today I started writing about a location within that desert which prompted me to ask what a desert made out of diamond look like?

I can't imagine that a diamond desert would be see through like glass. I'm thinking that the desert would be pure white. I'm guessing that would mean the desert would reflect an absurd amount of light, far more than just being all sparkly. I imagine maybe the sunglasses of my world may have been invented so people can traverse this desert.

Aside from diamond, I have been considering glass as a candidate for this deserts composition. My planet has a history of failed alien terraforming. Perhaps the desert was turned to glass after an incident involving some kind of heat based technology that accidentally turned the sand molten?

If all else fails, I suppose I could make up some fantasy substance for my desert, but that leaves me with my original question;

If there was a mountain/desert made of glass/diamond-like material, would it be see-through? White?

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    $\begingroup$ I'm also reminded that in Earth deserts, silica dust is an issue in storms. Diamond dust is going to be troublesome in engines and lungs... and possible more abrasive in the wind. $\endgroup$ Commented Nov 22, 2023 at 20:06
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    $\begingroup$ If it consists of small particles or crystals, then it would be pretty much like snow: each snowflake is transparent, but snow blanket is not transparent, it looks white because light is scattered and bounces off the ice crystals. $\endgroup$ Commented Nov 22, 2023 at 20:16
  • $\begingroup$ If you find glass (from bottles etc) on a beach(with wave action) that has been there awhile, the edges are all ground to frosted opaqueness, if its there long enough the whole piece of glass becomes that way.. $\endgroup$ Commented Nov 22, 2023 at 20:51
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    $\begingroup$ "The desert would reflect an absurd amount of light:" It cannot reflect more light than what is available, and plain ordinary sand already reflects some 80% of it. It won't be noticeably whiter than an ordinary desert of white sand. $\endgroup$
    – AlexP
    Commented Nov 22, 2023 at 21:38
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    $\begingroup$ Look at obsidian for what natural glass tends to look like, and how it tends to age and weather over geological periods of time. $\endgroup$ Commented Nov 23, 2023 at 3:44

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like normal mountains and deserts, no it will not be see-through

Mountains on earth are mostly made of quartz which is also transparent, are mountains see-through? impurities, crystal structure, fracture pattern, weathering, all of these will make it opaque.

These pebbles are made of transparent quartz but simple weathering has rendered them opaque. weathered surface is irregular and rough microscopically, which makes it opaque. You need to polish a material or otherwise render it perfectly smooth for something to be see-through. Sand in deserts is also made of quartz often individual grains are transparent but the net effect is not much like piles of transparent ice crystals forming snow.

enter image description here

Here is what a quartz crystal looks like.

enter image description here

Here is what a mountain made of quartz looks like.

enter image description here

here is what normal desert sand looks like under a microscope. Note each grain is transparent yet a desert made of sand is not.

enter image description here

for comparison this is what raw diamonds look like when washed and lightly polished, note again not transparent.

enter image description here

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    $\begingroup$ @Nelson source? diamonds are cheap and plentiful, it's only businesses that artificially keep their prices high. $\endgroup$
    – Pyritie
    Commented Nov 23, 2023 at 10:22
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    $\begingroup$ @Pyritie source? Unless you can regularly dig up gem-grade diamonds, where is "parts per billion in source rock" plentiful? $\endgroup$
    – Mutoh
    Commented Nov 23, 2023 at 12:36
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    $\begingroup$ @Mutoh Diamonds are not rare at all. They're just al bought up by two companies who control how much is released unto the market, creating an artificial scarcity. I've worked with a juweler, the ways you get F-ed in that branch are a lot more than you think. Quick google: thecuriouseconomist.com/are-diamonds-really-that-scarce $\endgroup$
    – Martijn
    Commented Nov 23, 2023 at 12:46
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    $\begingroup$ @Martijn diamonds are still "extremely rare" by geological standards, which is a far cry from "not rare at all". Otherwise, the monopoly wouldn't even be possible. $\endgroup$
    – Mutoh
    Commented Nov 23, 2023 at 13:13
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    $\begingroup$ There's a fundamental misunderstanding in your analogy to quartz: The opaque stones you picture are amorphous quartz, composed of microscopic crystals fused into a solid mass. These are white for the same reason sand made out of transparent grains is white. The transparent quartz crystals pictured are (probably, more or less) mono-crystalline, so they're translucent at the macro level. $\endgroup$ Commented Nov 23, 2023 at 21:48
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Let's pursue this from a "realistic" perspective, first.

Planets exist in geological time frames. That silica sand in terrestrial deserts didn't start out that way. Neither did your diamond deserts. Eons of time and erosion produced the sand.

Let's start with deserts

Silica is silicon dioxide. As mountains were ground down over millions of years, the silicon in those mountains absorbed oxygen to create the very stable silicon dioxide. We need to know this because it's our baseline for understanding what would happen with diamond and glass.

Diamond deserts? Not really

Diamond is just carbon. Carbon that's been subjected to high heat and pressure for those same millions of years, and then must be subjected to erosion for millions of years more. A planet with "diamond deserts" would be very old.

But, what do you get? A lot less diamond, I suspect, than you're thinking about. What you're going to get is carbon black (also known as carbon dust) with some of it siphoned off to create the gases carbon monoxide and carbon dioxide. Your deserts would look black. A very lovely black, though. At least as lovely as your space suit helmet will allow. I'm having trouble believing a planet with this much diamond would result in a breathable atmosphere.

I would expect to find an unusually high number of diamond rocks, though. What would they look like? They'd look like the dull crystal rocks that diamonds in the rough actually are. You don't get sparkly prism colors until you cut diamonds at the correct angles, and nature doesn't do that (if it does, I suspect it's really rare). You can see a wide variety of rough, glassy, natural diamond rocks at The Raw Stone.

OK, so what about glass?

Glass is even worse. It started as silica, was heated to a liquid and then re-poured into a convenient shape that we call "glass." What do you get when you erode it over millions of years? Yup, silica. When you walk in sand dunes today what you're walking on is your glass desert. Glass, silica... same thing.

OK, ignore the desert, what about mountains?

First, it's important to understand that mountains are anything but homogeneous. Even volcanoes, which have a very high percentage of obsidian and other volcanic rocks aren't just one thing. If you're imagining a single huge mountain-sized diamond, that's not what you'd have. A "diamond mountain" would be one that's predominantly made of diamond, in a variety of formations and sizes. To the best of our knowledge, nothing grows in just carbon black, so it's a good thing that your mountains also have other materials that eventually combine to create a real soil.

A glass mountain simply isn't realistic at all. I can't imagine how it would form naturally. You get small amounts of obsidian glass from volcanoes or small amounts of glass when lightning strikes silica, but mountain-sized amounts? Even predominantly? I can't see how it can be done. Even if it could, glass is very brittle, so it's hard to see the mountain staying a mountain very long, and if it appeared in the high heat/pressure conditions that form diamonds, it would melt.

OK, no mountains, no deserts... what if we toss reality to the wind? Let's invoke the engineers of Magrathea and just make mountains and deserts of diamond and glass. Who cares if they would only last a short while? Our world is brand-spanking new off the assembly line and orbiting a sun just like Sol. What would they look like?

If those engineers didn't cut any facets into the diamond mountain, it would look like a gigantic piece of what you saw when you clicked on The Raw Stone link, above. But if the engineers took the time to chisel those mountains so that facets were everywhere, what they'd look like after you put some sunglasses on would be a brilliant mind-blowing consciousness-expanding shower of every color you can imagine. It would be as breathtaking as it would be a danger to aerial navigation for hundreds of miles in any direction. I'd buy a ticket to see it.

The diamond deserts if uncut would be a milky color. Note that the many colors of raw diamonds come from contaminants. We're talking about the pure, undefiled beauty here. But if they were faceted... I doubt even sunglasses would save you. The desert would be a navigation hazard to space-faring vehicles. At least that's my opinion.

A glass mountain would be more translucent... but glass isn't perfectly light conductive. Looking at the mountain would give one the feeling that there's a lot of depth. It would be similar to looking into a deep lake of really clear water. You can sense that the water goes down a honking long way... but you can't actually see it. What you would "see" would be milky as the light would be refracted across the spectrum.

But a glass desert would be similar to a faceted diamond desert, but not as intensely brilliant. And unlike the diamond desert (in my opinion) the glass desert would be sharp. Wear tough shoes.

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  • $\begingroup$ Perhaps with enough storms you could have natural glassy deserts. A lot of wind constantly blowing fresh dust in the area and preventing rainfall there, constant lightning strikes converting that dust into glass. Getting enough storms but no rain seems fairly implausible but perhaps not completely impossible with geoengineering. $\endgroup$ Commented Nov 23, 2023 at 8:11
  • $\begingroup$ @ZizyArcher From a realistic perspective, you could never have enough lightning to overcome the wind and abrasive nature of silica. More to the point, glass is silica. If you have glass in a large enough "atomic unit" that you could tell it was glass, you wouldn't have a desert. You'd have (if you'll forgive the humor) a rock garden - aka a field of gravel, which I don't think is what the OP was looking for. Could be wrong, though. $\endgroup$
    – JBH
    Commented Nov 23, 2023 at 8:46
  • $\begingroup$ I believe glass chunks after lightning strike could be large enough to not move significantly despite constant wind - erosion of those wouldn't be THAT bad. Yeah hits of smaller sand grains would erode them slowly but if you somehow make enough storms you could end up with net glass gain, possibly ending with something resembling thick ice sheet (that is far less transparent than ice). You would get Antarctica-like desert except actually dry. $\endgroup$ Commented Nov 23, 2023 at 9:32
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    $\begingroup$ @ZizyArcher Lightning strikes, unfortunately, do not make transparent pieces of glass. Usually the result looks like fossilized piece of root, or a rock that has been oddly infected with a blisters. See eg. en.wikipedia.org/wiki/Fulgurite and en.wikipedia.org/wiki/Lechatelierite $\endgroup$ Commented Nov 23, 2023 at 9:35
  • $\begingroup$ desert sand is already made of faceted crystals, quartz, they just don't stay faceted as they bang agaist each other in the wind, so your desert is brilliant for a few years at best. $\endgroup$
    – John
    Commented Nov 23, 2023 at 13:15
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Compare with water ice

Water ice is known for being transparent. However it doesn't take much to get it less transparent such as a bucket of ice cube.

Such as most sheets of ice on puddles during winter. Black ice vs white ice on lakes. Most ends up being white ice due to snow, impurities, faults/fractures, inclusions, bubbles all contribute to making ice less transparent and more opaque.

Antarctica. Greenland

Large scale example is Antarctica or Greenland. Those are mountains and plains made of water ice. These represent the best case scenario of being mostly pure compared to other possible transparent materials, due to being formed from precipitation.

Minerals from crust.

Most other transparent materials will form from mixes within the crust. If the are forming from mixes they will rarely if ever transparent in bulk.

So transparent minerals such as diamond, corundum, silica, salt(NaCl), sucrose or etc. could form mostly pure mountains(given the right process). However when broken down into sand sized particles would resemble white sand beaches if mostly pure. Eg several white sand beaches are made of silica that if in large pure crystals would be transparent.

But for most part will look like rock/sand that we can see on Earth or like other mostly solid bodies in our solar system.

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You have a problem that none of the other answers have addressed:

Let's say you have this diamond mountain range. How it got there is not relevant, let's just assume it exists. You say that it eroded down to a diamond desert. This erosion presumably took place on geologic timescales, because eroding a mountain down to sand takes ridiculously long. (source: look at all the mountains we still have on Earth! They've been there for tens of thousands of years at the shortest, millions to hundreds of millions for most.)

But there's a problem with this: Under ordinary temperatures and pressures (e.g. on the surface of an earth-like planet), diamond does not remain diamond for more than a few millennia. It's well known among chemistry students that graphite is the lowest-energy allotrope of carbon at standard temperature and pressure, to the point that it's literally a textbook example of a very slow spontaneous transition.

Your mountain would turn into a mountain of graphite before it even had time to become a desert of diamond.

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  • $\begingroup$ Oh, neat. Anyone doesn't believe this effect exists, take a look at what melted sulphur does over a few hours/days. $\endgroup$ Commented Nov 23, 2023 at 21:15
  • $\begingroup$ My research says that the spontaneous diamond-graphite transition takes place on geologic timescales, the same as mountain erosion, and so you could very well get diamond sand. $\endgroup$
    – Mark
    Commented Nov 26, 2023 at 1:11
  • $\begingroup$ the oldest diamonds on earth are 3.3 billion years old, the transition is not that energetically favorable because there is a really high transition barrier, sp3 to sp2 carbon bonding has a very high kinetic energy barrier. So you need much higher than normal surface temperatures. Worse pressure prevents it or even reverses it and most of a mountain is under pressure. So NO the mountain is not turning to graphite except possibly on the erosional surface at the microstructure. so not that dissimilar to the clay conversion. $\endgroup$
    – John
    Commented Dec 14, 2023 at 21:44
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Captain W.E.Johns (the man who wrote the Biggles books) also wrote science fiction in the fifties. In his 'Now to the Stars' there was a glass planet. There is a picture on page 40 where they get a view through a clear section of glass down to the planet's molten core. This is pretty unlikely - ordinary glass is rarely pure enough to see through more than a foot of the stuff. It took a lot of fancy manufacturing to get fibre optics to get to kilometre distances. Water can be that clear, though.

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For a moment, we skip the process of forming your diamond deposits. This is chemically hard, but not impossible.

Diamond is able to BURN in a human-breathable atmosphere. Just like coal, it has somewhat higher calorific value than coal and will still produce the same carbon dioxide when burned.

It will readily burn in an atmosphere containing some oxygen even it is not really breathable.

Your desert made of diamond sand will burn down in an immense fire after the first source of ignition (a lighting will do). This is how coal deposits exposed to the surface end up burning down.

On the other hand, if your diamonds are this much abundant in your world, they may as well fuel the industrial revolution just like our coal did.

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  • $\begingroup$ When you say 'chemically hard' should that not be 'physically…'? $\endgroup$ Commented Nov 25, 2023 at 22:11
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    $\begingroup$ Diamond will not "readily" burn -- it takes a fair bit of provocation to get it to ignite. You'll note that the YouTube video uses a pure-oxygen atmosphere and a minute of heating using a propane torch to start burning the diamonds. $\endgroup$
    – Mark
    Commented Nov 26, 2023 at 1:20
  • $\begingroup$ @Mark The experiment on the video uses pure oxygen on a purpose. Otherwise, diamonds are not harder to ignite than anthracite or graphite. $\endgroup$
    – fraxinus
    Commented Nov 26, 2023 at 8:08
  • $\begingroup$ @RobbieGoodwin it is possible to produce diamond directly from carbon-containing substances without first creating graphite and then converting it into diamond. See e.g. "CVD diamonds". $\endgroup$
    – fraxinus
    Commented Nov 26, 2023 at 8:12
  • $\begingroup$ @fraxinus Thanks and that doesn't seem to address my query. If it does, why can you not Post a link to some specific reference to 'CVD diamonds'? Never mind, I'll take the trouble for you, and search the term myself. $\endgroup$ Commented Nov 27, 2023 at 21:30

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