Cave Sulfur

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

Collecting Cave Sulfur
The best way to collect the Cave Sulfur 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 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 Sulfur Plant will prevent the Crashfish from respawning, along with its powder.

A fifth suggestion is to use the Propulsion Cannon. Picking up the Crashfish and launching it will keep it away from the player. The Crashfish still is able to explode while being picked up.

Trivia

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