Blocks of Tourmaline can be mined or picked up by using Stone Mining Cells (or better).
Tourmaline blocks usually come in patches on the Lava layer - a few blocks are closely connected to each other embedded in the other typical rocks of these layers (Hardened Lava, Igneous Rock, Sulfur).
So if you see one block of Tourmaline in the walls of a Lava layer cave or find one by digging on this layer, best dig around it to collect more (similar to other uncommon blocks like Magnetite or Fossils).
Tourmaline can alternatively be obtained as a loot or pet-harvest from aggressive, but immobile Warmworms that can spawn on the Stalactite layer and on the Lava layer, on Siltstone, Stalactite rocks, Hardened Lava, Igneous Rock, Sulfur, Tourmaline, Diamond Nodes, Iron Nodes and other natural blocks from these layers in complete darkness.
So "farming" Warmworms will provide you with a larger amount of Tourmaline in a shorter timespan than by mining for it. However, some Caves on the Lava layer can also be quite rich in Tourmaline too, so exploring might be worth while as well.
The Lava layer can nowadays be mined with the help of Advanced Excavators too, but by that you will receive only half of the Tourmaline blocks that are removed like other common blocks, since Tourmaline is not an Node of Ore. If you use Advanced TNT (that was improved lately too), blocks from the Lava layer will simply be removed and deleted.
Blocks of Tourmaline can be placed into the world just as they are for decoration purposes, and can also be used for crafting. If you create a floor of an arena from blocks of Tourmaline, Warmworms and/or perhaps (more rarely) Hot Feet will spawn on these blocks in darkness; and also Treasure Chests might occasionally spawn in darkness additionally.
Obtaining a block of Tourmaline is one of the requirementes each to unlock the crafting recipes of Tourmaline Glass, Green Tourmaline Glass and Diamond Mining Cells. You only need to take one block of Tourmaline to partly unlock all these crafting recipes.
Tourmaline can be processed in the Processor to create 2 Crystal Shards each (used for some types of explosives like Explosive Bombs). Otherwise, Crystal Shards can also be obtained from Pigsies, Night Pigsies, Night Hoglets and sometimes from other creatures too, either when killing or pet-harvesting them.
1 (block of) Tourmaline can alternatively be hardened in the Forge (together with some Fuel) to receive 1 Infused Crystal, which will be required to craft Lumite Mining Cells - the best Power Cells available in Creativerse currently.
Warmworms can withstand sunlight, while Hot Feet or Mirus that tend to spawn in similar environments will burn away in the sun. So artificial biomes made of Hardened Lava and/or Igneous Rock built on the surface without ceilings can be very helpful. A significant amount of Warmworms and Hot Feet will spawn at large arenas of this type at night (plus very valuable Iron Treasure Chests too), but in the morning all the Hot Feet will burn away.
The same goes for arenas built from Siltstone or Stalactite where Mirus will spawn in darkness together with Warmworms (as well as Obsidian Treasure Chests), but the Mirus will burn away in the sunlight as soon as day dawns. However Siltstone and Stalactite usually make less Warmworms spawn than Hardened Lava and Igneous Rock...
You can kill Warmworms without being hit back by them if you simply place any type of block between your player character and the Warmworm, then you can whack it unfazed across the block while being shielded from any Warmworm counterattacks by the block. Not even the lava fountains that Warmworms can spit from time to time will hurt your player character in this case.
It's easy and painless to tame Warmworms by using the same trick. However please note that Warmworms will stay immobile as Pets too and cannot follow you after you've tamed them, because they are rooted into the ground and cannot move. Since a creature overhaul was done, you can't even set Warmworms to "follow" anymore either, so there are no tricks any longer to make them "take root" at another place.
So Warmworm Pets will just stay where you have tamed them, even if you remove the blocks that they are rooted in (often they will sink down in time in this case until they can reach another solid block, sometimes they might glitch upwards though...).
On older template worlds (RW1-4) you can also find Tourmaline on the deeper levels of the Stalactite layer underground that only need Obsidian Mining Cells to be harvested, while in RW5-8 worlds these uncommon rocks only very rarely occur anywhere else than on the Lava layer.