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NESOSILICATES

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Defnition

Greek, nesos, “island”silicates where the SiO4 tetrahedra

form isolated units

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Defnition

 Just like any other mineral containingradicals, the negatively-charged

radicals are held together yintervening cations !in red, at left"

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Olivine

#igh-$ igneous mineral, common in ma%cand ultrama%c rocks& commonly alters toser'entine

(itreous olive green !)g" to lack !*e"+uigranular to 'rismatic hait& 'oor

cleavageO'tics .olorless, ia/ial !0)g, -*e", mod1

high relief !n231", high 5(, δ  2167 !5nd order 8* colors".om'lete solid solution etween )g and *e

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Olivine

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Olivine

*orsterite!)g5SiO4"

*ayalite !*e5SiO4"

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Garnet

+uigranular, euhderal to suhedralhait& 'oor cleavage

O'tics .olorless, isotro'ic, highrelief !n231-319"

.om'le/ solid solutiongeneral formula :;<5Si;O35, where

: is a divalent cation !generally )g,*e, )n or .a" and < is trivalent!=sually :l, sometimes *e0;, $i, or

.r"

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Garnet

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Garnet

Pyrope(Mg3AlSi3O!"

Al#andine($e3AlSi3O!"

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Garnet

Spessartine(Mn3AlSi3O!"

Gross%lar(Ca3AlSi3O!"

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Garnet

Andradite(Ca3$eSi3O!"

&varovite(Ca3CrSi3O!"

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 Al%#inosili'ates (AlSiO"

)oderate to high grademetamor'hic minerals formed from

:l-rich source rocks:l in octahedral or a mi/ of

octahedral to tetrahedral sites

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 Al%#inosili'ates (AlSiO"

>yanite ? (itreous luish laded taletsw@ single 'erfect cleavage& # 7-

Sillimanite ? (itreous rown to greenclustered 'risms w@ single cleavage dir1

:ndalusite ? (itreous Aesh-red, reddishrown suare 'risms& # 17

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Al%#inosili'ates(AlSiO"

Andal%site Silli#anite

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Al%#inosili'ates(AlSiO"

)yanite

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Sta%rolite

)oderate to high grademetamor'hic mineral formed from

:l-rich source rocksBesinous to vitreous !dull when

altered" reddish-rown to rownishlack C-sided 'risms& commonlyforms inter'enetrating twins

O'tics <ia/ial!-", yellow 'leochroic,high relief !n2317", 5(DE5F-EEF

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Sta%rolite

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Sp*ene

.ommon accessory mineral in felsicigneous rocks and in some

metamor'hic rocksBesinous to adamantine gray, rown,

green, yellow or lack lens crystals&distinct diamond-sha'ed cleavage&# 7-717

O'tics <ia/ial!0", yellow 'leochroic,very high relief !n2516", 5(D5F,

D 613;

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Sp*ene

 $itanite