Celadonite is a mica , a phyllosilicate in both oxidation states, aluminium with formula K(Mg,Fe2+ )(Fe3+,Al)[Si 4O 10](OH) 2.
It crystallizes in the monoclinic system and usually forms massive aggregates of prismatic crystallites or in dull clay masses. It is soft with a Mohs hardness of 2 and a specific gravity of 3. Typically occurs as dull gray-green to bluish green masses. It forms vesicle fillings and linings in altered basaltic lavas.
It was first described in 1847 on Monte Baldo , near Verona, Italy celadon, for sea-green. It is one of two minerals, along with glauconite.
Common impurities are manganese and sodium (previously known as natrium).