This is probably one of the biggest spoilers in the game.  You can
attach up to 4 of them to your weapon and each one gives your weapon
+500 attack and you can make them once you get to the urssa lava caves
near the end of disc 1. First you need three items:

-Book of prophecies 1 (Shrine of Kaddan)
-Alcemy Stone (Desert where you meet the king)
-Spirit Stone (Mountains of Barr)

First take the book to the man in the Aquious library and he will join
you, hes an inventor, and send him to the workshop in Arygliph.  Keep
the Alcemy stone.  And with the spirit stone give it to the lady near
the place where you get the dragon flute and send her to the Arygliph as
well.  Now go back to Arygliph and exspand the workshop to have [lines,
Alchemy, and Syn]. Now you are ready to make them. Put the 2 new
inventors and maria on a line and set it to Alchemy, Original invention.
**THE PRICE MUST BE BETWEEN 5000 AND 5500**  now just create and sooner
or later you will have this amazing new stone that will make the game
much easier for all players especially undeveloped players.