Celadonite

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)[Si
₄O
₁₀](OH)
₂.

Celadonite
Green crystals of heulandite which owe their green colour to many tiny inclusions of celadonite
General
Category	Micas Phyllosilicate
Formula (repeating unit)	K(Mg,Fe2+ )(Fe3+ ,Al)[Si 4O 10](OH) 2
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	[1][2][3]

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. 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.

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