I REALLY LIKE PRISMARINE.

Just look at this sexy goodness.


And that is why I suggest adding prismarine shards to soul sand as an excavation drop.
Make it like minimum requirement is level 1000 in excavation or something. It should be a fairly low rate drop as well. We can't have it be too common now, can we? (As much as I'd love it to be common)

also ink sacs. Can't have dark prismarine without ink sacs. You could add those to soul sand as well. Soul sand is king. (although this is only secondary, although it would be nice, it's fairly easy to obtain ink sacs in the wild, so I don't believe it to be necessary.)

EDIT: The reason I want this is because I have a project that requires about 30k dark prismarine. And that's only the walls. It's a 400x400 town. There's simply not enough dark prismarine existing on the server to do what I want.

 

ugh wrong section. *pokes staff*

 

shards as common as slimeballs or glowstone dust.
crystals as common as.. nametags.
and ink sacs as common as eggs!

 

prismarine blocks do have a /sell value
lanterns don't.
and a lantern is worth $200 nowadays, not $500. and the price will only drop more as time goes on. The market is about as stable as the quartz market when it was first released.
Anyway, nametags are incredibly uncommon. less than 1% chance of dropping. The only thing rarer than nametags is cake.

You're really overestimating excavation here. Glowstone dust I get about 1 of every 6-12 blocks. nametags are rare, I get like 1 every 800-1000 blocks of dirt/grass. and eggs I get about 1 every 100-200.

So to get a single block of prismarine bricks I need to dig about 54-108 blocks of dirt. To get a stack that means 3456 - 6912 blocks of dirt.
To get a single lantern I need to dig at least 4000 blocks of dirt. and up to 5000. It's SUPER rare.

Now take into account that it's soul sand. It only appears in relatively small quantities compared to dirt. And to prepare a large amount of soul sand manually takes a lot of time. And that's why I think the chances I want are fine to use.