I made 2 mil gil yesterday doing nothing but mining for 2 hours.
Catalysts on my server are insanely expensive for some reason... even though they are easy as **** to get. I went to Dragonhead, mined Fossilized Matter for not that long (well about 2 hours) had a stack and a half (almost 2 stacks). Well they sell for over 7k gil each on my server... which is completely ridiculous considering how easy they are to get. I just put all of them up for sale at wards along with all the mythril/silver I got... they all sold.
Fossilized Matter sell fast.. they are what you use to double/triple meld your Int/Str/whatever materia.