As per issue #3932 We're also unable to chisel Prismarine, Diamond and Emerald blocks.
You can chisel them if you take a pre-chiselled block from creative mode but cannot chisel the standard block.

A few lines down prismarine 1 and 2 are still disabled. So you can chisel the prismarine but not to dark or brick

A problem everybody should be aware of is that these blocks are broken in the iChisel GUI. You can't chisel the vanilla blocks, and you can't make the chiseled blocks vanilla. You need to put them on the ground and left click, or use the regular chisel GUI. Something to do with having two chisel block groups.

And I did see that prismarine was intentionally disabled in this commit to fix duping prismarine shards with the uncrafting table. Just a few lines down in 'scripts/crafttweaker/integrations/mods/chisel.zs'. But imo, it's not worth disabling blocks over a few prismarine shards when the uncrafter can turn string into superium.

Oh that makes sense. I had accidentally left those lines commented out when I tried your fix. Works great so far.

I just fixed diamond and emerald blocks and opened a pull request. Looking at prismarine now while I'm waiting on paperclips

could you link the PR or tell me how you updated it so I can update this for my server.

I just fixed diamond and emerald blocks and opened a pull request. Looking at prismarine now while I'm waiting on paperclips

#4604
It's only two lines.
In your instance folder, open 'scripts/crafttweaker/_globals/chiselBlocks.zs', and make a newline at line 81 with
<minecraft:diamond_block:0>,
and at line 105 with
<minecraft:emerald_block:0>,

Hey @eturner could I also add Prismarine the same way you did diamonds and emerald blocks?

#4604
It's only two lines.
In your instance folder, open 'scripts/crafttweaker/_globals/chiselBlocks.zs', and make a newline at line 81 with
<minecraft:diamond_block:0>,
and at line 105 with
<minecraft:emerald_block:0>,

Hey this worked a charm. To also fix prismarine In your instance folder, open 'scripts/crafttweaker/integrations/mods/chisel.zs', add this at line 78 and 79

// Add Prismarine
Carving.addVariation("prismarine", <minecraft:prismarine:0>);

this still isnt fixed ;-;