This coin is a worthless cull. Totally ruined, no detail remaining! And I'm keeping it.

[Finn235]

Sometimes when buying large lots, you will get coins like this

This AE20 was probably a Greek coin at some point judging by the thickness (and weighing in at probably 8g before losing so much of the patina) and coins like this tend to just get passed around and around, used only to bump up the coin count in lots and entice bidders to bid just a little higher. As I was prepared to carry on the tradition, I noticed the tiniest little sparkle on the coin and decided to give it a closer look and then research what I saw.

On one side, there are two crystals, one whitish and one more clear (difficult to see in the photo) which I believe are cerussite (PbC03) - a natural lead ore, probably originatinf from impurities in the coin, or something lead touching it in the ground.

On the other side is a reddish black crystal which I believe is cuprite (Cu2O), a natural ore of copper

Neither of course will restore any numismatic value to the coin, but I still think it's interesting enough to hold on to. I tend to forget while collecting XF denarii just how long 2,000 years really is. To overly-romanticize the whole thing, it made me stop and think about all the work that went into mining and refining and minting this coin, only for nature to return those metals back to their natural state.

Anywho, anyone else have coins with cool mineral/crystal growths on them? Post 'em up!

[JayAg47]

This fourree Tiberius denarius got some copper sulfate growing out from one of its exposed core. Along with a tiny red crystal that shines under sun light (looks better in hand than photo). 

here’s a closer look 

 

 

 

Edited September 24, 2023 by JayAg47

[Severus Alexander]

Wow, that coin looks like a 3D relief of an alien moon!

I immediately think of Chinese coins for this sort of thing.  Definitely some sort of crystally thangs going on here, on this early Chinese bronze cowrie:

 

Must be some interesting minerals on this heavy (9.45g) early Qin ban liang, c. 350-300 BCE:

 

And for a different sort of adhesion, check out the actual ancient fabric at the top of the reverse of this Han ban liang (H7.17, c. 175-120 BCE):

[hotwheelsearl]

Alexandrian tets often have nice minerals. This has some blue azurite. I would have posted a close up, except I appear to have LOST all of my tets. Cannot find them anywhere. This makes me extremely sad.

[Finn235]

26 minutes ago, Severus Alexander said:

Wow, that coin looks like a 3D relief of an alien moon!

I immediately think of Chinese coins for this sort of thing.  Definitely some sort of crystally thangs going on here, on this early Chinese bronze cowrie:

 

Must be some interesting minerals on this heavy (9.45g) early Qin ban liang, c. 350-300 BCE:

 

And for a different sort of adhesion, check out the actual ancient fabric at the top of the reverse of this Han ban liang (H7.17, c. 175-120 BCE):

I'll need to hunt down the picture, but probably about 6 years ago I bought 200ish Song dynasty cash from Lanz's ebay shop with the intent of making a collection of it. Sat on it for a year, realized that Chinese didn't "click" for me outside of Wang Mang's coinage, and I sold most of them to an interested local collector on FB marketplace. One of the coins was completely encrusted in this absolutely stunning electric blue azurite like that Ban Liang, but brighter. I regret that I sold that one.

[hotwheelsearl]

Chinese coins always seem to have some crazy colors.

 

This song dynasty 10 cash has the works - malachite, azurite, and cuprite!

 

[Finn235]

Found it - remembered I had downloaded it off of CCF to post on CT a few years ago. Not even sure which emperor this one is, but this was the actual in-hand appearance of the blue Song Cash

[John Conduitt]

I haven't kept a coin only because of the deposits, but this one comes close. I don't know what these minerals are but they seem to appear regularly on coins (as above), so are presumably copper-based - cuprite (Cu2O) and malachite (Cu2CO3(OH)2), together with blue, yellow and green toning?

Commodus Denarius, 186-187

Rome. Silver, 18mm, 2.75g. Laureate head right; M COMM ANT P FEL AVG BRIT. Felicitas, draped, standing left, holding caduceus in right hand and sceptre in left hand; PM TR P XII IMP VIII COS V PP (RIC III, 143)

[Ocatarinetabellatchitchix]

10 hours ago, Finn235 said:

Anywho, anyone else have coins with cool mineral/crystal growths on them? Post 'em up!

Bought a hoard of slugs, not sure if Roman or Greek since the legends are unreadable. Under microscope, just not sure either what these mineral deposits are.

[Nerosmyfavorite68]

I bought this Caracalla Tetradrachm because it was uncleaned.  The white stuff at the top of the bust is actually a bit glossy.  It reminds me a lot of calcite, seen in mine exploration videos of wet mines.

\

I bought this inexpensive throw-in, because of the verdigris.

 

Patina is also mineralization.  It's just (sometimes) prettier.

Purchased 100% for the patina.

 

Ditto:  I don't know if the unusual, variegated patina was caused by the cleaning process, but it was inexpensive and interesting enough to plop into the basket.

 

[CPK]

@Nerosmyfavorite68 That Byzantine's patina is a stunner!

[CPK]

Here's my contribution. This coin is actually in really good shape, but it's got scattered deposits/mineral growths that make it even more interesting. I especially like the reddish deposit on the obverse that serves as Kore's eye, and the large inset "emerald" at 7 o'clock on the reverse. 😉

[Ancient Coin Hunter]

This Titus tet of Alexandria has some rust colored encrustation on obverse and reverse. I imagine more of the coin, due to the pitting was encrusted before some sort of harsh cleaning. Don't know by whom or what exactly is the nature of the mineral...

 

[Orange Julius]

I’ve always liked this one, not because of the coin but because of the mineralization showing the shape of other coins laying on it within the hoard.

Edited September 24, 2023 by Orange Julius

[robinjojo]

Interesting thread and great coins!  

The oxidation process, where the metals are exposed to air, water and other chemical, converts these metals to their oxide/sulfide forms, probably as they were before extraction and refining.  The exception are metals found in their native state. such as silver and copper.  Gold is always in its native state, since it does not oxidize.

Azurite

I created a thread on CT dealing with this subject back in September 2020.

https://www.cointalk.com/threads/the-beauty-of-impermanence.367521/

We have oxidation to thank for the wonderful patinas on our bronze and silver coins, an attribute that greatly increases the beauty and value of a coin when it is at its best, such as an even emerald green patina on a Roman sestertius.  Even oxidation creating multi-color earthen patinas can be very impressive.

Fausta, AE 18, Thessalonica Mint, 326-328 AD.

 

 

 

Edited September 24, 2023 by robinjojo

[hotwheelsearl]

I found my tets! I tend to go for the ones with all the minerals rather than the ones with just the bronze.

 

these two have some amazing azurite crystals, combined with cuprite and malachite. I wonder why Egyptian (and Chinese!) coins tend to have this mineralization more than coins of other regions.