Cryas can only contain one type of eleth at a time and usually take on the color of the type contained within them. Larger pieces of cryas seem to have something of an expiration date, as there's references made to cryas that are no longer able to absorb eleth.
 It is a Mystery
While one of the panels in the Records Room in Telos Astue clearly says that cryas is artificial ore, there are numerous references made throughout the game that make it sound like cryas is a naturally occurring substance that one can simply find on the ground or even mine. Is it a plot hole, or could cryas also be a natural substance as well as artificial?