Do diamonds erode?
March 4, 2013 2:53 PM   Subscribe

My girlfriend says if water is constantly flowing over a diamond eventually it will break down and apart. I say that because diamonds are harder than anything that might be in water, they are immune to such erosion and weathering. She says that's idiotic, and BOY does that grind my gears! What do you think, green?
posted by lain to Science & Nature (25 answers total) 4 users marked this as a favorite
 
Interestingly enough, there's a thing called marine diamonds which are washed from their origin point into the ocean where they become part of the sedimentary layers (from which they are then mined).

Diamonds are the hardest substance known to exist, but they are brittle when fractures and inclusions exist in their structure. All of the erosional and weathering processes the diamonds go through cause a great deal of stress on the structure. As a result, many of the imperfect stones are destroyed during their journey from the kimberlite to the ocean.
posted by jamaro at 3:04 PM on March 4, 2013


Water regularly erodes hard things over time. Look at the Grand Canyon for example. I'm sorry but your girlfriend is correct.
posted by 2bucksplus at 3:04 PM on March 4, 2013 [2 favorites]


Hardness and erosion are different things. Hard things erode at a slower rate than soft things. That diamonds are the hardest known material does not mean they are "immune" to erosion.
posted by dfriedman at 3:07 PM on March 4, 2013 [8 favorites]


"Hard" means that they will scratch other surfaces, and are difficult to scratch themselves. That doesn't mean they're indestructible — as crystals, they cleave on regular axes. So yeah, they'll still be vulnerable to erosion — not as much as, say, sandstone, but they'll still be imperfectly formed crystals subject to stress and fracture like anything else.
posted by klangklangston at 3:08 PM on March 4, 2013 [1 favorite]


This comment by someone who produces waterjet cutting machines might be useful.
posted by HuronBob at 3:09 PM on March 4, 2013


Water has been called the "universal solvent." It will take diamonds a long time to erode, but they will eventually.
posted by The Light Fantastic at 3:09 PM on March 4, 2013


There are lots of folks who are unpleasantly surprised when they realize they've busted their diamond jewelry by dropping it or accidentally smacking it against something. DeBeers would have you believe that diamonds are forever, but in truth, any idiot with a hammer could split one by hitting it at the right angle.
posted by Diagonalize at 3:11 PM on March 4, 2013 [3 favorites]


Diamonds are pure carbon. In proper conditions they can burn, and when exposed to water which contains dissolved oxygen, they will oxydize slowly. The resulting CO2 turns to carbonic acid and is carried away by the water.
posted by Chocolate Pickle at 3:11 PM on March 4, 2013 [5 favorites]


Lol! As a geologist these answers are cracking me up. Is this really an argument about wearing weddings rings or something?

Your girlfriend is kinnnd of right, but who has billions of years to find out? The diamond might turn back into graphite first.
posted by cakebatter at 3:12 PM on March 4, 2013 [28 favorites]


Also your understanding of erosion IS wrong. Hard stuff in water is not what makes things break apart.
posted by cakebatter at 3:14 PM on March 4, 2013 [3 favorites]


In addition to the issues described above, if there is any kind of sand or other particle in the water (which there always is in rivers), the particles will erode.

Here is a paper that touches on the subject (in which they sandblast diamond and related materials).

But all of this will happen very, very slowly.
posted by ssg at 3:14 PM on March 4, 2013


Placer mining of diamonds works because diamonds are not eroded by water. In other words, when water erodes the rock surrounding a diamond, the water carries the diamond along until it ends up getting deposited in sediment.

Yes, diamonds are brittle - you could easily smash one to bits with a hammer. However, being broken up is not the same as being eroded. You could also combust it with heat.

A water jet cannot be used to cut diamond or tempered glass.

Water has been called the "universal solvent."

Not by anyone who was awake in high school chemistry class. A diamond will not dissolve in water. The reason is that water is polar and carbon is not. The diamond (or graphite of any pencil) is held together with covalent bonds, not ionic bonds. Other things that don't dissolve in water: fat-soluble vitamins. Water not being a universal solvent is why drinking glasses full of water do not fall apart in your hand.

This is a purely academic question that is of no practical consequence to someone who owns diamond jewelry.
posted by Tanizaki at 3:22 PM on March 4, 2013 [13 favorites]


That you can't water jet cut tempered glass has nothing to do with how hard the glass is but rather the fact that when you relieve the internal tension of the sheet by cutting through it the rest of the sheet fractures into a gazillion pieces.
posted by Mitheral at 3:37 PM on March 4, 2013 [2 favorites]


If you bet your girlfriend that she could subject a diamond to flowing water and not see any erosion in her lifetime, your money would be safe.
posted by Danf at 3:49 PM on March 4, 2013 [1 favorite]


Diamonds are held together by very strong bonds. They are not immune to change, but the change they undergo under normal, Earth-surface conditions, is not going to be from weathering. Everything else weathers around them -- that's why you get them showing up on beaches in Africa.

They won't stay in the state they're in forever -- but the changes they'll undergo will not be from solubility in water. Ultimately they're just a bunch of carbon atoms held together with very strong bonds. Put in enough energy, and the bonds will break. Water, however, does not contain anywhere near the required energy level.
posted by DoubleLune at 5:48 PM on March 4, 2013 [1 favorite]


Diamond is kinetically stable but thermodynamically unstable. This means that the carbon in a diamond would rather be in a lower energy state (e.g., carbon dioxide), but the barrier to reaction is so high that the rate of reaction is incredibly slow.

From a thermodynamics standpoint, it doesn't matter how hard diamond is or whether it is nonpolar compared to water; the free energy is in favor of reaction. On a long enough timescale, diamond will react with oxygen and other chemicals found in water, and thus be eroded. But the kinetics of the reaction mean that, at ambient temperatures and pressures, these reactions will occur so rarely as to be negligible on human timescales.

As a thought experiment, your girlfriend is right. From a practical standpoint, you are right (though your reasoning is imprecise).
posted by dephlogisticated at 6:44 PM on March 4, 2013 [2 favorites]


Water regularly erodes hard things over time. Look at the Grand Canyon for example. I'm sorry but your girlfriend is correct.

The Grand Canyon is not made out of solid diamond. It is primarily many layers of sedimentary rock, which is relatively easy to erode due to water. Sandstone is porous, and calcium-rich minerals such as limestone are dissolved by slightly acidic water. It does not make any sense to compare the Grand Canyon to a diamond. If the rocks there were full of diamonds, they would have been eroded out of the sedimentary rocks (as they erode out of kimberlite) and been washed into placer deposits. So if you are talking about diamonds eroding like the Grand Canyon and on the same time scale, no, not possible.
posted by oneirodynia at 6:54 PM on March 4, 2013 [3 favorites]


I was curious about the "universal solvent" thing and searching via Google Books it does appear to be a common appellation for water. Here it is in a CK-12 Foundation chemistry textbook, for example.
posted by XMLicious at 7:51 PM on March 4, 2013 [3 favorites]


Feet walking on a stone staircase eventually wear the steps down and make them curved. That doesn't mean shoe soles are harder than stone or that you could scratch stone with a piece of shoe leather.

At the atomic level everything is worn by whatever rubs against it, even if it takes a long time for this slow wear to be visible to the naked eye.
posted by w0mbat at 9:42 PM on March 4, 2013 [2 favorites]


As usual people are taking extreme sides. Can you provide some more information: over what time period are you talking? Years, thousands, millions of years?
posted by devnull at 1:20 AM on March 5, 2013 [1 favorite]


Diamonds are pure carbon. In proper conditions they can burn, and when exposed to water which contains dissolved oxygen, they will oxydize slowly. The resulting CO2 turns to carbonic acid and is carried away by the water.

I agree with this. I also agree that this would take far longer than a lifetime to test in natural circumstances. From the wikipedia article: Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions.

Maybe if you had a waterjet machine and a hunk of diamond, and a really precise scale (or an electron microscope?), you could test this.

tl;dr: you're both right. Nothing is permanent, given enough time. But diamond is definitely on the long side of the bell curve of things that don't erode.
posted by gjc at 4:14 AM on March 5, 2013


I was curious about the "universal solvent" thing and searching via Google Books it does appear to be a common appellation for water. Here it is in a CK-12 Foundation chemistry textbook, for example.

That is fine as far as it goes for K-12 students, but it does not tell us about the actual solvent abilities of water. As the linked text notes, there are still many things that water does not dissolve despite the popular appellation. The majority of your body's mass is water yet your body is remarkably not dissolved.
posted by Tanizaki at 7:06 AM on March 5, 2013


Tanizaki: That is fine as far as it goes for K-12 students, but it does not tell us about the actual solvent abilities of water. As the linked text notes, there are still many things that water does not dissolve despite the popular appellation. The majority of your body's mass is water yet your body is remarkably not dissolved
... at least, not faster than your body's cells are built, used, and replaced during your lifetime.

Pretty sure skin, hair, teeth, and bones will dissolve if left in water for centuries, even without microbial activity.
posted by IAmBroom at 10:09 AM on March 5, 2013


Pretty sure skin, hair, teeth, and bones will dissolve if left in water for centuries, even without microbial activity.

When you understand why oil does not dissolve in water, you will understand why your sureness is misplaced. Some of those things may disintegrate in water, but they will not dissolve. (there is a difference) If you want to dissolve hair and skin, you are going to need Nair.
posted by Tanizaki at 1:54 PM on March 5, 2013


Ah, Tanizaki, you caught me being lazy. Yes, those materials will probably not dissolve entirely.

All of those things will disintegrate in water because parts of them will dissolve. The enamel of teeth (hydroxylapatite) is probably the least soluble of all. Skin cell walls are made of a variety of slightly-soluble organic compounds. Once the walls are broached, much of the interior cell protoplasm (which solubilithologists refer to as "goo") is of course water-soluble.
posted by IAmBroom at 10:03 AM on March 6, 2013


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