>

Diamonds are not rare at all, especially in space. There is a red dwarf in Centauri constellation that compressed itself into 2500 mile diamond.
This is a friendly reminder to read our rules.
Remember, /r/Showerthoughts is for showerthoughts, not "thoughts had in the shower!"
(For an explanation of what a "showerthought" is, please read this page.)
Rule-breaking posts may result in bans. >

Very true. 
There are four "green sand" beaches in the world.  The green comes from olivine (peridot) mixed in with the sand.  Tiny crystals, to be sure, but plentiful. >

Even without considering other planets, diamonds are not all that rare compared to other gemstones. The De Beers company used a number of methods, some rather shady and unsavory, to artificially inflate their value. >

We can also artificially make diamonds. Can't artificially make insects trapped in amber >

I mean…you can… >

Exactly. That's what Tuesday afternoons are for. >

Or perhaps the DNA itself is the true value? Perhaps varied DNA samples are cosmic currency, that would make earth a giant bank….. >

Considering scientists have found over a thousand alternatives to DNA, all carbon-based, maybe it's just life that's valuable. >

The idea that a diverse databank of what are essentially “blueprints” to create a life form is the principle; a  plant or animal may have a relatively short life, but being able to re-create them would be invaluable. You make a good point though, not all life forms may have DNA, whatever building blocks of life exist would be the currency. >

If you had an interstellar trading partner, it would already reduce the rarity of your item. >

Diamonds are just slightly fancy rocks. The only reason they are considered to be as valuable as they are considered to be, is because of marketing by DeBeers, the people who have basically a monopoly on diamonds on this planet. >

One of the reasons we use artificial diamonds in industry nowadays. >

And why everyone should be using artifical diamonds anyway.
They're likely more pure, cheaper, and don't have the blood of child slaves on them. >

I thought you meant just on earth, because I can imagine there are many amber pieces with unique examples of insect species >

I wish I still knew where it was, but back in the 90's during the height of Jurassic Park mania, I bought a piece of amber with a small mosquito in it because, I mean, what kid wouldn't want to have that when you're a huge JP fan?!?
Anyways, I still remember what it cost at the gem store. $30. >

Yes I've always thought that anything durable of biological origin like coral, wood, bone, fossiliferous stone would be valuable in interplanetary trade.  I imagine some  alien potentate impressing their guests with a dinner table top of solid earthwood (assuming these aliens are made of meat). >

Right but what's the relevance of including stuff the other side of the galaxy? Cool that it exists and all, but scarcity is for all practical purposes defined by how easy the resource is to actually get hold of (much like oil reserves in utterly inaccessible locations don't count for much) >

If interstellar trade ever becomes possible, and gemstones and gold are that abundant, I wonder what the new precious metals and gems will be? Maybe some new ones we haven’t discovered yet? >

If/when interstellar trade becomes a thing the only things that will be worth anything. Like very strong (and quite possibly synthetic) alloys, or DNA samples for research. >

Phosphorus is probably the rarest life-necessary element, even accounting for how relatively little we require. Hydrogen, oxygen, carbon, these are easy to get. Many of the trace metals are abundant in asteroids. If we're looking to have the most people possible then phosphorous is likely the limiting factor, and therefore likely to be relatively high value. 
Probably not as high value as intellectual materials. In a universe of interstellar travel so much abundance of materials should likely exist that things such as art, music, books, dance, and other such things will probably become our most valuable exports. >

It is clear that only organic or intellectual property will be valuable at some point. I was referring more "alloys" as stuff that can only be made and not occurring naturally, possibly lab grown. But yes that is like intellectual property in the sense that it can only be made and could originate from a specific culture for specific reasons. >

It’s true, but as valuable as dried bug collection or botanical collection, not just amber. Clear epoxy will do even better.
In space where life is rare, oddities of alien life for sure will be valuable among species. I would like an alien bug in epoxy too. >

I get it, but in whatever’s perspective? Maybe if there are aliens, they might consider it valuable, otherwise matters are just a bunch of atoms slapped together. >

Food is just a bunch of atoms slapped together, your brain is just a bunch of atoms slapped together, doesn't make either of them less important. >

Yea but you eat brain for energy and use your food to think so it’s a little different >

if we gave a shit about rarity then diamonds wouldnt be worth anything >

Diamonds are the hardest natural substance, which means they're more durable in jewelry than any other gemstones. A Diamond will last much longer than a ruby or sapphire.