How to obtain
Harvesting from Pet Warmworms will provide you with a larger amount of Tourmaline in a shorter timespan than mining for it.
However, some Caves on the Lava layer can also be quite rich in Tourmaline too, so exploring these can be worthwhile as well, especially while killing all the Warmworms that spawn in there at the same time.
On older worlds RW1-RW4, Tourmaline can also be found occasionally on the Stalactite layer and more rarely on the Corruption layer. Mining through the Stalactite layer will not even cause a Lumite Mining Cell to lose durability.
Tourmaline blocks usually come in batches 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).
Blocks of Tourmaline can be mined or picked up when having a Stone Mining Cell (or any better Power Cell) equipped. Diamond Mining Cells and Lumite Mining Cells will not lose durability when mining Tourmaline blocks alone.
However, to dig through walls of the Lava layer in order to reach Tourmaline blocks that are embedded between Hardened Lava, Igneous Rock and Sulfur, at least an Iron Mining Cell (or better) needs to be equipped. Even the best Power Cells lose durability when mining through the Lava layer.
The Lava layer can be mined with the help of Advanced Excavators too, but these will save only half of all the rather rare Tourmaline blocks that the Excavators remove, just like all the other more common blocks, since Tourmaline is not an Node of Ore.
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.
Warmworms do not always drop Tourmaline, but when they do, you can collect a significant amount from them at a time - either 5 or sometimes even 10 blocks.
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.
Harvesting from Warmworm Pets is the best option to collect a lot of Tourmaline. Taming Warmworms can be done absolutely safely after placing just one block between your player character and a Warmworm, the same trick as for hunting them, which is easy and painless.
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. They will sink down in this case - sometimes only when you leave the area or relog - until they can reach another solid suitable natural block where they will then stay.
In order to receive the best possible pet-harvest, you will then need to feed each hungry Warmworm its favorite type of Food as shown in its pet window when activating the pet Warmworm by pointing your cursor at it and then either clicking the right mouse button or typing "f" (as the default key). Warmworms are hungry as soon as you have tamed them and will display a food icon in their thought bubble and pet window.
A while later, when your Pet Warmworms have digested the Food and will display a Mining Cell / ArcTek Gauntlet in their thought bubble and pet window, you can harvest from them by pulling them with the gauntlet (no Mining Cell is required). You'll need to wash them with a Washer if you wish for them to get hungry again so you can repeat the harvesting cycle.
How to use
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 requirements 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.
Crystal Shards are mainly used to craft Explosives like Explosive Bombs, but also other high-tier crafts. However, Crystal Shards can also be obtained from Pigsies, Night Pigsies, Night Hoglets and occasionally from other Creatures too, either by killing or pet-harvesting.
1 (block of) Tourmaline can be hardened in the Forge (together with some Fuel) to receive 1 Infused Crystal, which is required to craft Lumite Mining Cells - the best Power Cells available in Creativerse.
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 the newest game worlds RW5-RW8, these uncommon rocks only very rarely occur anywhere else than on the Lava layer.