- You have struck orthoclase!
Orthoclase is a common yellow stone which conveniently happens to be magma-safe. Along with microcline, it is one of the most common types of stone most players will encounter.
 In Real Life
Orthoclase, a potassium-aluminum silicate, is an Alkali feldspar mineral that forms in relatively moderate temperature for an igneous mineral, between 500 and 900 degrees centigrade. Orthoclase's chemical formula is identical to that of Microcline (KAlSi3O8), but Microcline forms at lower temperatures (usually below 400 degrees centigrade). Gem quality Orthoclase is one of two minerals that are called Moonstone.
used with kaolinite sometimes for ceramics