Cave Sulfur

Cave Sulphur is a sulfur-based raw material that has a chance to be found in Crashfish Plants after the residing Crashfish has left. The PDA description states it has the chemical formula SO4Tr.

It can be used for crafting the Repair Tool and Flares.

Cave Sulphur collecting
The best way to collect the Cave Sulphur is to lure the Crashfish out of the plant, evade its explosion (using the Seaglide), and return to its nest for the powder.

Likewise, luring out the Crashfish and triggering it to dash towards the player will cause it to gain momentum. Swimming towards it will cause the Crashfish to overshoot and explode, dealing no damage to the player if the maneuver is executed properly.

An alternative is to use the upgraded Repulsion Cannon to push them against a wall or far away from the player, triggering their explosion which will deal no damage to the player due to the distance.

Additionally, one can use a Stasis Rifle to immobilize it. However, the Crashfish will still explode even when being frozen by the stasis field, so it is recommended to stay out of the blast radius. Destroying the Crashfish Plant will prevent the Crashfish from respawning, along with its powder.

The powder is not a guaranteed find in every Crashfish Plant. There could also be an egg in the plant or nothing at all.

Trivia

 * The Cave Sulphur's former name was Crashfish Powder.