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Formula: Ca2Al3[Si2O7][SiO4]O(OH)
Sorosilicate (Si2O7 groups) epidote group,
paramorph of
clinozoisite.
Replacement of Al by Fe3+ is usually less than 10%, so there is no solid solution series all the way to
epidote group
(R&M 86:5:452)
Varieties
Tanzanite is the deep blue gem variety of zoisite. The colour is caused by traces of
vanadium V3+
as well as chromium and strontium.
Specific gravity: 3.15 to 3.36
Hardness: 6 to 7
Streak: White
Colour: Colourless, purple, greyish-white, grey, yellowish-brown, yellow, pink (due to the presence of manganese)
(R&M 86:5:452), green
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid
Common impurities: Fe,Mn,Mg,Cr,Ti,Ca,Na,V,Sr,H2O
Environments:
Pegmatites
Metamorphic environments
Zoisite is a rock-forming mineral that occurs fairly commonly in medium-grade
regionally metamorphosed calcareous
shale and sandstone, and in
amphibolite resulting from the regional metamorphism of basic igneous rocks.
It is also occasionally found in low-grade thermally metamorphosed impure
limestone and skarn,
(R&M 86:5:452) and in
pegmatites.
Zoisite may be found in
sandstone,
shale,
limestone,
skarn,
schist,
amphibolite and
eclogite.
It is a mineral of the blueschist,
eclogite),
greenschist,
amphibolite and
granulite facies.
Localities
The Merelani Hills, Simanjiro district, Manyara region, Tanzania, tanzanite crystals occur in highly metamorphosed
graphite
gneiss with diopside,
pyrite, quartz,
grossular, dolomite,
calcite, prehnite,
graphite, zeolites,
alabandite and wurtzite. Mineral inclusions
found in tanzanite include graphite,
actinolite, calcite,
diopside, gypsum,
ilmenite, quartz,
rutile, titanite and
xenotime
(R&M 94.6.530-536).
Alteration
Zoisite can form from hydrothermal alteration of calcium-rich
plagioclase.
(R&M 86:5:452)
grossular and lawsonite to
zoisite, prehnite and H2O
Ca3Al2(SiO43 + 3CaAl2(Si2O7)(OH)2.H2O ⇌
2Ca2Al3[Si2O7][SiO4]O(OH) +
Ca2Al(Si3Al)O10(OH)2 +10H2O
Increasing temperature faours the forward reaction
(SERC)
kyanite and zoisite to anorthite,
corundum and H2O
2Al2O(SiO4) + 2Ca2Al3[Si2O7][SiO4]O(OH)
⇌
4CaAl2Si2O8 + Al2O3 + H2O
The equilibrium temperature for this reaction at 5 kbar pressure is 480oC
(greenschist facies), and at 10 kbar it is about
720oC (amphibolite facies). The equilibrium is to
the right at higher temperatures, and to the left at lower temperatures
(SERC, AM61.699-709).
kyanite and zoisite to margarite
and anorthite
2Al2O(SiO4) + 2Ca2Al3[Si2O7][SiO4]O(OH)
⇌ CaAl2(Al2Si2O10)(OH)2 +
Ca(Al2Si2O8)
The equilibrium temperature for this reaction at 6 kbar pressure is about 520oC
(amphibolite facies), and at 9 kbar it is
about 675oC (amphibolite facies). At any pressure the equilibrium
is displaced to the right at higher temperatures, and to
the left at lower temperatures
(SERC, AM61.699-709).
kyanite, zoisite and
diaspore to margarite
Al2OSiO4 + Ca2Al3[Si2O7][SiO4]O(OH) + 3AlO(OH) ⇌
2CaAl2(Al2Si2O10)(OH)2
Increasing temperature favours the forward reaction
(SERC)
kyanite, zoisite and
quartz to anorthite and H2O
Al2OSiO4 + 2Ca2Al3[Si2O7][SiO4]O(OH) + SiO2 ⇌
4Al2OSiO4 + H2O
Increasing temperature favours the forward reaction
(SERC)
lawsonite to margarite,
zoisite and wairakite and H2O
6CaAl2(Si2O7(OH)2.H2O ⇌
CaAl2Si2Al2O10(OH)2 +
2Ca2Al3[Si2O7][SiO4]O(OH) +
Ca(Si4Al2)O10.2H2O + 8H2O
Increasing temperature favours the forward reaction
(AM61.699-709).
lawsonite to zoisite, kyanite,
quartz and H2O
4CaAl2(Si2O7)(OH)2.H2 ⇌
2Ca2Al3[Si2O7][SiO4]O(OH) + Al2OSiO4
+ SiO2 + 7H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 500oC
(greenschist facies), with the equilibrium to
the right at higher temperatures, and to the left at lower temperatures
(AM61.699-709).
lawsonite to zoisite, margarite,
quartz and H2O
5CaAl2(Si2O7)(OH)2.H2 ⇌
2Ca2Al3[Si2O7][SiO4]O(OH) +
CaAl2(Al2Si2O10)(OH)2 + 2SiO2 + 8H2O
The equilibrium temperature for this reaction at 6.5 kbar pressure is about 425oC
(greenschist facies), with the equilibrium
to the right at higher temperatures, and to the left at lower temperatures
(AM61.699-709).
lawsonite and corundum
to zoisite,
kyanite and H2O
4CaAl2(Si2O7)(OH)2.H2 + Al2O3
⇌ 2Ca2Al3[Si2O7][SiO4}O(OH) +
2Al2OSiO4 + 7H2O
The equilibrium temperature for this reaction at 15 kbar pressure is about 570oC
(eclogite facies), with the equilibrium to
the right at higher temperatures, and to the left at lower temperatures
(AM61.699-709).
lawsonite and grossular to
zoisite, quartz and H2O
5CaAl2(Si2O7)(OH)2.H2O + Ca3Al2(SiO43 ⇌
4Ca2Al3[Si2O7][SiO4]O(OH) + SiO2 + 18H2O
Increasing temperature favours the forward reaction
(SERC)
lawsonite and margarite to zoisite,
kyanite and H2O
3CaAl2(Si2O7)(OH)2.H2 +
CaAl2(Al2Si2O10)(OH)2 ⇌
2Ca2Al3[Si2O7][SiO4]O(OH) + 2Al2OSiO4
+ 6H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 500oC
(greenschist facies), with the equilibrium to
the right at higher temperatures, and to the left at lower temperatures
(AM61.699-709).
margarite to corundum, zoisite,
kyanite and H2O
4CaAl2(Al2Si2O10)(OH)2 ⇌ 3Al2O3
+ 2Ca2Al3[Si2O7][SiO4]O(OH) + 2Al2OSiO4
+ 3H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 650oC
(amphibolite facies), with the equilibrium to
the right at higher temperatures, and to the left at lower temperatures
(SERC, AM61.699-709).
margarite and quartz to zoisite,
kyanite and H2O
4CaAl2(Al2Si2O10)(OH)2 + 3SiO2 ⇌
2Ca2Al3[Si2O7][SiO4]O(OH) +
5Al2OSiO4 + 3H2O
The equilibrium temperature for this reaction at 8 kbar pressure is about 510oC (amphibolite facies), with the
equilibrium to the right at higher temperatures, and to the left at lower temperatures
(AM61.699-709).
prehnite to zoisite,
grossular, quartz and H2O
5Ca2Al(Si3Al)O10(OH)2 ⇌
2Ca2Al3[Si2O7][SiO4]O(OH) + 2Ca3Al2(SiO43 +
3SiO2 + 4H2O
Increasing temperature favours the forward reaction
(SERC)
prehnite and lawsonite to
zoisite, quartz and H2O
Ca2Al(Si3Al)O10(OH)2 +
2CaAl2(Si2O7)(OH)2.H2O
⇌ 2Ca2Al3[Si2O7][SiO4]O(OH) + SiO2 + 8H2O
Increasing temperature favours the forward reaction
(SERC)
magnesium-rich tremolite, zoisite,
corundum and H2O to tschermakite
3☐Ca2MgSi8O22(OH)2 +
2Ca2Al3[Si2O7][SiO4]O(OH) + 7Al2O3 + H2O ⇌
5☐Ca2(Mg3Al2)(Si6Al2)O22(OH)2
(AM 76.990)
wairakite to zoisite and
margarite and quartz and H2O
5Ca(Si4Al2)O10.2H2O ⇌
2Ca2Al3[Si2O7][SiO4]O(OH) +
CaAl2Si2Al2O10(OH)2 + 12SiO2 + 8H2O
Increasing temperature favours the forward reaction
(AM61.699-709).
wairakite, zoisite and
margarite to anorthite and H2O
Ca(Si4Al2)O10.2H2O + 2Ca2Al3[Si2O7][SiO4]O(OH)
+ CaAl2Si2Al2O10(OH)2 ⇌ Ca(Al2Si2O8) +
H2O
Increasing temperature favours the forward reaction
(AM61.699-709).
zoisite to anorthite, grossular,
corundum and H2O
6Ca2Al3[Si2O7][SiO4]O(OH) ⇌
6CaAl2Si2O8 +
2Ca3Al2Si3O12 + Al2O3 + 3H2O
The equilibrium temperature for this reaction at 6 kbar pressure is about 760oC
(amphibolite facies), and at 10 kbar it
is about 950oC
(granulite facies). For any given pressure, the reaction goes to
the right at higher temperatures, and to the left at lower temperatures.
(SERC)
zoisite and kyanite to
margarite and anorthite
2Ca2Al3[Si2O7][SiO4]O(OH) + 2Al2OSiO4 ⇌
CaAl2(Al2Si2O10)(OH)2 + 3Al2OSiO4
Increasing temperature favours the forward reaction
(SERC)
zoisite, kyanite and quartz to
anorthite and H2O
2Ca2Al3[Si2O7][SiO4]O(OH) + Al2OSiO4
+ SiO2
⇌ 4Ca(Al2Si2O8) + H2O
The equilibrium temperature for this reaction at 10 kbar pressure is about 690oC
(amphibolite facies), with the equilibrium to
the right at higher temperatures, and to the left at lower temperatures
(SERC, AM61.699-709).
zoisite, kyanite and diaspore to
margarite
Ca2Al3[Si2O7][SiO4]O(OH) + Al2OSiO4 +
3AlO(OH) ⇌ 2CaAl2(Al2Si2O10)(OH)2
The equilibrium temperature for this reaction at 12 kbar pressure is about 480oC
(blueschist facies), with the equilibrium to
the right at higher temperatures, and to the left at lower temperatures.
(SERC)
zoisite, margarite and quartz to
anorthite and H2O
2Ca2Al3[Si2O7][SiO4]O(OH) +
CaAl2(Al2Si2O10)(OH)2 + 2SiO2 ⇌
5Ca(Al2Si2O8) + 2H2O
The equilibrium temperature for this reaction at 6 kbar pressure is about 540oC
(amphibolite facies), with the equilibrium to
the right at higher temperatures, and to the left at lower temperatures
(SERC, AM61.699-709).
zoisite and quartz to grossular,
anorthite and H2O
4Ca2Al3[Si2O7][SiO4]O(OH) + SiO2 ⇌
Ca3Al2Si3O12 + 5CaAl2Si2O8
+ 2H2O
The equilibrium temperature for this reaction at 5 kbar pressure is 650oC
(amphibolite facies), with the equilibrium to
the right at higher temperatures, and to the left at lower temperatures
(SERC).
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