Clinozoisite

Clinozoisite is a complex calcium aluminium sorosilicate mineral with formula: Ca₂Al₃(Si₂O₇)(SiO₄)O(OH). It forms a continuous solid solution series with epidote by substitution of iron(III) in the aluminium (m3 site) and is also called aluminium epidote.[1]

Clinozoisite
Clinozoisite
General
Category	Sorosilicates Epidote group
Formula (repeating unit)	Ca2Al3(Si2O7)(SiO4)O(OH)
Strunz classification	9.BG.05a
Dana classification	58.2.1a.4
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/m
Unit cell	a = 8.879, b = 5.583 c = 10.155 [Å]; β = 115.50°; Z = 2
Identification
Color	Colorless, green, gray, light green, yellow green, pink
Crystal habit	Elongated primatic crystals, striated; granular to fibrous
Twinning	Lamellar on {100} uncommon
Cleavage	Perfect on {001}
Fracture	Irregular/uneven
Tenacity	Brittle
Mohs scale hardness	6-7
Luster	Vitreous
Streak	Grayish white
Diaphaneity	Transparent to translucent
Specific gravity	3.3 - 3.4
Optical properties	Biaxial (+)
Refractive index	nα = 1.706 - 1.724 nβ = 1.708 - 1.729 nγ = 1.712 - 1.735
Birefringence	δ = 0.006 - 0.011
2V angle	14 to 90° measured
References	[1][2][3]

Clinothulite is a manganese bearing variety with a pinkish hue due to substitution of Mn(III) in the aluminium site.[4]

It was originally discovered in 1896 in East Tyrol, Austria, and is so-named because of its resemblance to zoisite and its monoclinic crystal structure.[1]

It occurs in rocks which have undergone low to medium grade regional metamorphism and in contact metamorphism of high calcium sedimentary rocks. It also occurs in saussurite alteration of plagioclase.[2]

Jadeite bearing pyroxene minerals have suggested Clinozoisite and paragonite are associated and derived from lawsonite releasing Quartz and water via the following reaction:[5]

${\displaystyle {\ce {4CaAl2Si2O8(H2O)2 + NaAlSi2O6 <=> 2Ca2Al3Si3O12(OH) + NaAl3Si3O10(OH)2 + SiO2 + 6H2O}}}$