Soul Gems can be used in many custom recipes.
They can also be used for the Soulless title with a cost of 2000 Soul Gems in /ccraft
You can obtain Soul Gems from opening keys at /crates or from daily/weekly chests! You can also get them from your daily log-in reward as well at /spawn!
Soul Gems can also be combined with 8 gems for easier storage!
You can do so by using /condensecustom while the gems are in your inventory.
If you want them back to normal, use /uncondensecustom while the Condensed Soul Gem is in your inventory!