Celadonite is a mica group mineral, a phyllosilicate of potassium, iron in both oxidation states, aluminium and hydroxide with formula K(Mg,Fe2+)(Fe3+,Al)[Si4O10](OH)2.

It crystallizes in the monoclinic system and usually forms massive aggregates of prismatic crystallites or, more commonly, in dull clay masses.

Early research suggests this mineral has ties to weakly metamorphosed plutonic rocks during formation, and is also found with montmorillonite clays or zeolite crystals.

[5] Association with zeolites may indicate these minerals favor the same underlying conditions of crystal growth.

It is one of two minerals, along with glauconite, used in making the pigment known as green earth,[6] which was an important pigment for the decoration of Joseon buildings (so much so that the only site which produces celadonite in South Korea is a designated natural monument).