- You have struck microcline!
Microcline is one of the most common stone types found in Dwarf Fortress, showing up pretty much everywhere. Its distinct cyan color is shared only by raw adamantine and ice.
 In Real Life
Microcline is the low-temperature form of alkali feldspar. It is a potassium aluminum silicate with a chemical formula of (KAlSi3O8). Orthoclase is a mineral of the same composition that forms at higher temperatures.
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However, those learned in the obscure ways of the mysterious and arcane claim that it is in fact the best mineral in the game, but in disguise. Even adamantine quakes at the existence of this material, as it is the highest value and most diverse material in the game.
Or at least, it's meant to be. Due to a bug in Toady's coding, Microcline actually doesn't have its special pop up window necessary for its status (much like that of adamantine) and the game also does not switch to "Royal" mode, where the game swaps from ASCII into the real graphics, groundbreaking 3D environments, with hi-definition models and excellently simulated physics. Microcline is also, due to a misplaced 0 (or a googol of them) not the highest value, although it should be. Toady has received many angry complaints about this mistreatment of the wonderful Microcline, which is still noted at every point the player discovers a vein of it. Many new players assume Microcline to simply be a common stone type, with no special qualities. Little is it known that originally Microcline was intended to be adamantine, as well as the jail of the HIDDEN FUN STUFF!
used with kaolinite sometimes for ceramics