Those with odd items such as Strange Volcanic Rock, Strange Mineralized Water , Strange Oceanic Sediment and no idea what purpose they serve
From wowhead –
These are part of your weekly quest that awards rep . This can be started with a short questline . Players may come across lesser benethic arcanocrystal from opening treasures. If a player receives this item, they will be directed to a cave in Azshari Terrace at (60,32) called Mardivas’s Laboratory. Upon turning in the quest, players can then pick up a quest where they must defeat an elemental amalgamation. Once the amalgamation has been defeated, players can then pick up the quest the laboratory of mardivas where they must empower either a lesser Arcanocrystal, greater Arcanocrystal, or both and then defeat an enemy.
Apparently this seems to be only be able to be done weekly
Further down page in comments someone said
“In addition to the once a week summoning in the Laboratory, all of the Arcane Reagents are barter items at vendors later on (rep gated) to upgrade Essences, the one’s I’ve seen are 20x of any given one. For those thinking there are so many and they can’t possibly be used – hold on to them.”
Accurate or not I’m not sure but hang on to them anyway
An achieve is also available here – Periodic Destruction
From wowhead-
So, how this achievement works – At the Laboratory of Mardivas, there is a weekly quest (The Laboratory of Mardivas) where you can summon an elemental and defeat it. Sometimes mobs in Nazjatar can drop Arcane Reagents that can be used at the laboratory to create different creatures: Strange Volcanic Rock (which I will be referring to as Fire), Strange Mineralized Water (Water) and Strange Oceanic Sediment (Sand). Benthic items with the Elemental Instincts effect grant an increased chance of looting these reagents from Nazjatar mobs.
There are 6 crystals where you can input reagents on, 3 greater crystals and 3 smaller crystals, and for each creation, you can add a reagent to either 1 smaller crystal, or 1 smaller and 1 greater crystal. After inputting any combination you’d like (or none at all), you create the elemental by confirming your choice in the Essence Amalgamator next to the crystal clusters.
This achievement requires you to invoke and defeat every single combination of elementals that can be created in the laboratory. You can only summon an elemental once a week yourself (if you die, the elemental despawns, but you can simply re-create the creature in the essence amalgamator, not losing your reagents in the process) There are 13 different elementals that need to be created
It seems if you accept the weekly quest when entering the cave and complete it – you wont get option to do the achieve bit so be careful when accepting quest
No reagent = Arcane Amalgamation
Small Water = Watery Amalgamation
Small Fire = Burning Amalgamation
Small Sand = Dusty Amalgamation
Small Sand, Great Sand = Herald of Salgos
Small Sand, Great Water = Spawn of Salgos
Small Sand, Great Fire = Salgos the Eternal
Small Water, Great Water = Osgen
Small Water, Great Sand = Zomera
Small Water, Great Fire = Omus
Small Fire, Great Fire = Ungormath
Small Fire, Great Water = Xue
Small Fire, Great Sand = Moghiea
Guide here –
https://www.wowhead.com/achievement=1…/periodic-destruction…
None the Wiser Guild 