Celadonite

Not to be confused with Caledonite.

Celadonite is a mica group mineral, a phyllosilicate of potassium, iron in both oxidation states, aluminium and hydroxide with formula K(MgFe³⁺◻)(Si₄O₁₀)(OH)₂.

Celadonite
Green crystals of heulandite which owe their green colour to many tiny inclusions of celadonite
General
Category	Phyllosilicate minerals, mica group, celadonite subgroup
Formula	K(MgFe3+◻)(Si4O10)(OH)2
IMA symbol	Cel[1]
Crystal system	Monoclinic
Crystal class	Spheroidal (2) (same H-M symbol)
Space group	C2
Identification
Color	Blue-green to olive to applegreen
Cleavage	perfect on {001}
Tenacity	Fragile
Mohs scale hardness	2
Luster	Waxy, dull, earthy
Diaphaneity	Translucent
Specific gravity	2.95 - 3.05
Density	2.95 - 3.05
Optical properties	Biaxial (-)
Pleochroism	Visible
2V angle	5°- 8°
Common impurities	Mn, Na, Ca
Other characteristics	Radioactive 9.11% (K)
References	[2][3][4]

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 basaltic lavas. 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 French celadon, for sea-green. 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).^[7]

Common impurities are manganese, calcium and sodium (previously known as natrium).