framework silicates 2/3 of crust is framework silicates 2/3 of crust is framework silicates quartz...
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Framework SilicatesFramework Silicates 2/3 of crust is framework silicates2/3 of crust is framework silicates Quartz and feldspars are most commonQuartz and feldspars are most common All with similar structuresAll with similar structures
TO4 tetrahedral frameworkTO4 tetrahedral framework T = Si or AlT = Si or Al Each oxygen is shared with another Each oxygen is shared with another
tetrahedrontetrahedron Sharing of highly charged cation (SiSharing of highly charged cation (Si4+4+) make ) make
open structuresopen structures
Consequences of open Consequences of open frameworkframework
CompostionalCompostional Accommodate large cations – Ca, Na, Accommodate large cations – Ca, Na,
and Kand K Charge balance maintained by Charge balance maintained by
exchange of Al and Siexchange of Al and Si
Physical propertiesPhysical properties Specific gravity lower than most other Specific gravity lower than most other
mineralsminerals E.g. quartz = 2.65, olivine = 3.27E.g. quartz = 2.65, olivine = 3.27 Not stable at high PNot stable at high P Restricted to crustRestricted to crust
Four major groups:Four major groups: Silica group (SiO2)Silica group (SiO2) FeldsparsFeldspars FeldspathoidsFeldspathoids ZeolitesZeolites
Silica groupSilica group Eight possible polymorphsEight possible polymorphs one other synthetic varietyone other synthetic variety
Rare forms – High PRare forms – High P Stishovite – Si in octahedral coordinationStishovite – Si in octahedral coordination CoesiteCoesite
Common formsCommon forms Quartz, Quartz, Tridymite, Tridymite, Cristobalite, Cristobalite,
Fig. 12-1Fig. 12-1
StructuresStructures
Reconstructive polymorphism Reconstructive polymorphism between qtz, tridymite and between qtz, tridymite and cristobalitecristobalite
Displacive polymorphism between Displacive polymorphism between and and varieties varieties
Tridymite and Cristobalite not stable Tridymite and Cristobalite not stable at surface P and Tat surface P and T Will convert to quatzWill convert to quatz
Varieties of quartzVarieties of quartz
Microcrystalline varietiesMicrocrystalline varieties Chert – occurs as nodules or beds in Chert – occurs as nodules or beds in
limestonelimestone Black version – flintBlack version – flint Red version – jasperRed version – jasper
Chalcedony – fibrous microcrystalline Chalcedony – fibrous microcrystalline quartzquartz
Color bands or irregular color called agateColor bands or irregular color called agate
Coarsely crystalline Coarsely crystalline varietiesvarieties
Amethyst – biolet or purple from trace Amethyst – biolet or purple from trace amounts of Feamounts of Fe
Rose quartz – pink colored, may be caused Rose quartz – pink colored, may be caused by mineral inclusionsby mineral inclusions
Citrine – yellow quartz from Fe, radiation or Citrine – yellow quartz from Fe, radiation or combinationcombination
Smoky quartz – irradiation and small Smoky quartz – irradiation and small amounts of Alamounts of Al
Milky quartz – minute fluid inclusionsMilky quartz – minute fluid inclusions
Feldspar GroupFeldspar Group
Three compositional end membersThree compositional end members K-feldspar (KAlSiK-feldspar (KAlSi33OO88) – Ks or Or) – Ks or Or
SanidineSanidine OrthoclaseOrthoclase MicroclineMicrocline
Albite (NaAlSiAlbite (NaAlSi33OO88) – Ab) – Ab Anorthite (CaAlAnorthite (CaAl22SiSi22OO88) – An) – An
Plagioclase – An and AbPlagioclase – An and Ab Alkali – Ab and Ks (Or)Alkali – Ab and Ks (Or)
Plagioclase feldsparsPlagioclase feldspars
At high T, continuous solid solutionAt high T, continuous solid solution CaAl substitutes for NaSiCaAl substitutes for NaSi Generally described as fraction of An, Generally described as fraction of An,
assuming An + Ab = 100%assuming An + Ab = 100%
Compositions divided into ranges and Compositions divided into ranges and given namesgiven names Albite: An0 – An10Albite: An0 – An10 Oligoclase: An10 – An30Oligoclase: An10 – An30 Andesine: An30 – An50Andesine: An30 – An50 Labradorite: An50 – An70Labradorite: An50 – An70 Bytownite: An70 – An90Bytownite: An70 – An90 Anorthite: An90 – An100Anorthite: An90 – An100
Alkali feldsparsAlkali feldspars
Continuous solid solution at high TContinuous solid solution at high T K and Na same charge – K and Na same charge –
compensates for difference in sizecompensates for difference in size K and Ca don’t have solid solution K and Ca don’t have solid solution
because different size and chargebecause different size and charge
Fig. 12-5Fig. 12-5
Names of compositional variations caused by solid solution in feldspar minerals
Influence of temperature on the allowed solid solution of feldspar minerals
Fig. 5-23Fig. 5-23
Origin of miscibility gap – variations in solid solutions
FeldspathoidsFeldspathoids
Similar to feldsparsSimilar to feldspars Common mineralsCommon minerals
Nepheline NaNepheline Na33K(AlK(Al44SiSi44OO1616)) Leucite KAlSiLeucite KAlSi22OO66
Sodalite group NaSodalite group Na88AlAl66SiSi66OO2424ClCl22 Nepheline is the most commonNepheline is the most common
Chemically different from feldsparsChemically different from feldspars Less Si relative to Na and KLess Si relative to Na and K Rarely found with quartz (too much Si)Rarely found with quartz (too much Si) Found in alkali-rich, silica poor igneous Found in alkali-rich, silica poor igneous
rocksrocks
Structurally similar to feldsparsStructurally similar to feldspars 4 and 6 member rings4 and 6 member rings Linked to form frameworkLinked to form framework More open than feldsparsMore open than feldspars Lower specific gravity than feldsparsLower specific gravity than feldspars
Feldspathoid minerals compared to feldspars minerals Shaded regions are allowed solid solution
ZeolitesZeolites
Very common group of mineralsVery common group of minerals Over 40 naturally occurring varietiesOver 40 naturally occurring varieties Over 600 synthetic onesOver 600 synthetic ones Largest single group of silicate Largest single group of silicate
mineralsminerals Most commonly alteration products of Most commonly alteration products of
basaltic and andasitic volcanic rocksbasaltic and andasitic volcanic rocks
Commonly too fine grained for Commonly too fine grained for identification from physical identification from physical propertiesproperties Requires x-ray diffractionRequires x-ray diffraction Often considered “clay minerals’Often considered “clay minerals’
Tectosilicates, not phyllosilicatesTectosilicates, not phyllosilicates
CompositionComposition
Hydrated framework silicatesHydrated framework silicates General formulaGeneral formula
MMxxDDyy(Al(Alxx+2ySi+2ySin-x-2yn-x-2yOO2n2n) MH) MH2200 Si/Al ratio varies from 1 to 6Si/Al ratio varies from 1 to 6 M usually monovalent Na or KM usually monovalent Na or K D usually divalent Ca, Mg or othersD usually divalent Ca, Mg or others
StructureStructure Open framework of Al/Si tetrahedralOpen framework of Al/Si tetrahedral Link to form open channels and voidsLink to form open channels and voids Geometry varies from one to the otherGeometry varies from one to the other Water and cations often in voids and Water and cations often in voids and
weakly bondedweakly bonded Create important properties of mineralsCreate important properties of minerals
Fig. 12-22Fig. 12-22
Heulandite
OccurrenceOccurrence
All but analcime are secondaryAll but analcime are secondary Analcime may be a primary igneous Analcime may be a primary igneous
mineral, late crystallization in basaltsmineral, late crystallization in basalts Can be used as low-T Can be used as low-T
geothermometersgeothermometers
Variety of UsesVariety of Uses
Desiccants: hydrated, but water easily Desiccants: hydrated, but water easily exchanges so can dessicate gasses such exchanges so can dessicate gasses such as COas CO22, freon, and organic chemicals, freon, and organic chemicals
Molecular sieves: if dehydrated, other Molecular sieves: if dehydrated, other molecules fill voids, e.g. separate N from molecules fill voids, e.g. separate N from O, purify OO, purify O
Water softener: Na-rich zeolites will Water softener: Na-rich zeolites will remove Ca from water and replace with remove Ca from water and replace with NaNa
Water purification: heavy metals in Water purification: heavy metals in acid mine drainage, isotopes from acid mine drainage, isotopes from radioactive waste, contaminated radioactive waste, contaminated soils, remove NHsoils, remove NH44 from wastewater from wastewater and cat litterand cat litter
Soil conditioner: agriculture for water Soil conditioner: agriculture for water and cations, slow release of N, carrier and cations, slow release of N, carrier of pesticidesof pesticides
Feed: pigs, cattle, chicken, turkeys, Feed: pigs, cattle, chicken, turkeys, improve feed efficiency, reduce improve feed efficiency, reduce waste smell, increase N retentionwaste smell, increase N retention
Petroleum refining, cleaning spills, Petroleum refining, cleaning spills, filters in paper processingfilters in paper processing
Environments of formation (increasing Environments of formation (increasing depth of burial)depth of burial) Weathering with high pHWeathering with high pH Diagenesis of ash, lakes and marineDiagenesis of ash, lakes and marine Alteration from ground waterAlteration from ground water Hydrothermal alterationHydrothermal alteration Contact metamorphismContact metamorphism Burial and low grade regional Burial and low grade regional
metamorphismmetamorphism