It crystallizes in the monoclinic system and usually forms massive aggregates of prismatic crystallites or, more commonly, in dull clay masses. It is soft with a Mohs hardness of 2 and a specific gravity of 3. It forms vesicle fillings and linings in altered basalticlavas. 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.[5]
It was first described in 1847 on Monte Baldo, near Verona, Italy. The name is from the Frenchceladon, for sea-green. It is one of two minerals, along with glauconite, used in making the pigment known as green earth.[6]
