Materias are a good way to improve your gear or make money in Final Fantasy XIV as there are often players buying them.
But how do you get materias easily? On top of the clusters you can exchange for materia there's an option you might have missed, directly in your inventory.
In fact, every piece of equipment you own has a level of Spiritbond, this level is written in the item's description and increases the more you play with that gear equipped.
When the Spiritbond hits 100% you can then right-click on the item and select "Extract Materia" to obtain a random materia.
Extracting a Materia will reduce the level of spiritbond to 1% but don't worry, playing with the gear will increase its level again, and it's quite fast so don't hesitate to check regularly to get the most materia out of your equipment.