Speaking of this, I used to make myself a nice pile of change just with a stack of fire + lightning crystals when I'd run around Starfall Hillock in Sarutabaruta.
The crawlers drop a rare/ex meteorite (plus silk threads, duh) for a quest that a 62 alchemist turns into 3x/6x/9x glass fiber, the Yagudo necklaces desynth into copper ingots w/lightning, and I'd randomly steal cotton off mandys/stab Tom Tit Tat in the face for Fruit Punches. Some of the laziest moneymaking I've ever done, but for someone who wants to farm their own minnows, it's actually rather nice (long as you can synth the meteorite on the spot). Sure, it's not "I caught a fish and made a fuckton of Gil", but if you're making your own, you can get all the materials in one place faster than randomly dropping bugbears/moblins or stacks of flint stones.
XI Wiki


with the glass fiber and copper ingots.