Clinozoisite

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

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.

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

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.

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.

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

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

References

• Nesse, William D., "Introduction to Mineralogy," (c)2000 Oxford University Press ISBN 0-19-510691-1