So, the recent birthstone-related promotions (ruby, peridot) have minerals in the promotion art, and then those reminded me of them shard bombs.

Oh shard bombs, sad sad shard bombs. There have been an enormous number of threads discussing their issues in the past. This thread isn't about those issues. For this thread, we can either change the mechanics of the existing bombs (not my preference, but plausible) or add a new branch of the existant alchemy paths that require ancient shells. Why tortodrone stuff? Because I am inspired by a certain mechanic that the tortodrone guns have, but don't utilize for various dmg and attack style related reasons. Besides, having a bomb line for tortodrones would be pretty fun for many players.

The mechanic: the crystals seem to be a physical barrier in addition to being painful to touch.

Why not have a "shard" bomb family that can do this as well? Same ring pattern, just not as much damage as the fists (or their shard bomb siblings), because it's easier to put down where you want and this is a mechanic that's been perfected for use with these bombs, so one would use them for that mechanic and little else. Also, no knockback and no initial center dmging explosion, just an animation to "grow" the cage. The crystals could be a bit fatter to make a complete cage with a single bomb, and last:

----2-3x as long as the tortofist crystals do (perhaps even longer if the bomb is heated)
----Or last forever until the enemy or attack of any kind (enemy or player) collides with/touches them at least 3x, similar to how mineral spires take 3 hits to be destroyed, but I could see bomb spam being a huge issue with that.
----Another alternative is to simply have a planted ring last forever, but instantly decay the second another bomb of the same family from the same user (emphasis on same user) is placed.

It is likely this mechanic would have no effect on bosses, so the shards would need to do some sort of damage in general, not just be a cage.

As to whether or not touching these barriers would deal significant dmg, or perhaps even inflict status, I'll leave that up to discussion. I'm more interested in the mechanic, but I think the same "ouchie to touch" effect the tortoguns have would be fine. Exploding after would be fun and work well with timed option #3. But if we like that, please no knockback. I do not like knockback. My middle name is "NoKnockbackNova." Okay no it's not. Back to the cage mechanics:

Enemies within would be unable to exit, enemies outside would be unable to enter (unless is boss). Projectiles would be unaffected. So, cage your team up and shoot out, or trap monsters. Of course, in PvE, the crystals do not hinder player movement. But in PvP? Oh yes they would. Dashing would allow the player to pass crystal barriers, and interestingly, cloaked players are not hindered either - I like to think we are so good at parkour when in "ninja mode," we don't even see ourselves do the flips to get past stuff. So, keep players off points, or trap them in their locker room, create bottlenecks? I don't play PvP, but I like to think about these things - which is why the above timed/3x touch/forever-unitl-another-bomb choices above are important, regarding the duration of planted crystals.

I think this sort of thing would be very interesting. It would be quite different from the usual dmg-bomber behavior (every monster follow in my painful footsteps! Ignore everybody else please!) but I could definitely see using it to control groups of enemies in confined areas, especially for missions like Grinchlin Assault, or to easily create a safe haven from annoying explodey-souls or other swarming threats like minis in compounds.

A torto-sword version of this mechanic could simply be a very low damage brandish style charge that grows crystal barriers up in a straight line, probably shorter than the current 5* brandish burst. It would be cool to have swords that look like the tortoguns... Hmm. Punching regular attack? Another thread sometime later perhaps! But it would be another of many.