Silica mineralsSilica minerals Quartz (alpha <573Quartz (alpha <573ooC <beta C <beta

<870). Change is total but the <870). Change is total but the shape of the beta form is shape of the beta form is preserved in lavaspreserved in lavas

Cristobalite & Tridymite are high Cristobalite & Tridymite are high temp forms but most common as temp forms but most common as devitrification products of devitrification products of obsidian (e.g spherulites)obsidian (e.g spherulites)

Coesite, the high pressure form, Coesite, the high pressure form, occurs in impact-site rocksoccurs in impact-site rocks

Opal is a cryptocrystalline form Opal is a cryptocrystalline form of cristobalite with sub-of cristobalite with sub-microscopic water-filled pores microscopic water-filled pores that make up 5-10%that make up 5-10%

CarbonatesCarbonates Calcite Calcite CaCOCaCO33 Limestone and carbonatites Limestone and carbonatites

Aragonite CaCOAragonite CaCO33 (orthorhombic) High P,low T mm (orthorhombic) High P,low T mm

DolomiteDolomite CaCOCaCO33.MgCO.MgCO3 3 LimestoneLimestone

AnkeriteAnkerite CaCOCaCO33.(Fe,Mg)CO.(Fe,Mg)CO3 3 Ore deposits in limestoneOre deposits in limestone

SideriteSiderite FeCOFeCO33 Rare sedimentary rocks Rare sedimentary rocks

Ultra thin-polished section of calcite showing twinningCalcite cement in sandstone

Garnet XGarnet X33YY22SiSi33OO1212

CaCa33AlAl33 grossulargrossular calc-silicate metamorphic rockscalc-silicate metamorphic rocks

FeFe33AlAl33 almandinealmandine meta-mudstones, med-high grademeta-mudstones, med-high grade

MnMn33AlAl33 spessartinespessartine meta-mudstones, low grademeta-mudstones, low grade

CaCa33FeFe33 andraditeandradite skarns skarns

MgMg33AlAl33 pyropepyrope meta-basalts especially high-Pmeta-basalts especially high-P

A few granites/rhyolites have almandine/spessartine garnet. A few granites/rhyolites have almandine/spessartine garnet. Some mantle peridotites have pyrope-rich garnetSome mantle peridotites have pyrope-rich garnetGarnet in S-type granite Garnet with inclusions in gneiss

Apatite and zirconApatite and zircon Apatite CaApatite Ca55(PO(PO44) ) 33(OH,F,Cl) Holds (OH,F,Cl) Holds

most of the P in rocks. Forms needles most of the P in rocks. Forms needles in many igneous rocks. Small triangular in many igneous rocks. Small triangular grains in metamorphic. Some shells grains in metamorphic. Some shells and some marine pttes in sedimentary and some marine pttes in sedimentary rocksrocks

Zircon ZrSiOZircon ZrSiO44 Holds most of the Zr in Holds most of the Zr in most rocks. Very stable so most rocks. Very stable so concentrates in sand. Very high melting concentrates in sand. Very high melting point and many granites have “restitic” point and many granites have “restitic” (unmelted) zircon that has retained an (unmelted) zircon that has retained an earlier U/Pb isotopic age. 420 Ma earlier U/Pb isotopic age. 420 Ma Lachlan Fold Belt Granites have Lachlan Fold Belt Granites have zircons that can be as old as 3000Mazircons that can be as old as 3000Ma

Zircon with zoning &Laser ablation holes

Andalusite Sillimanite KyaniteAndalusite Sillimanite Kyanite In meta-shales (excess of In meta-shales (excess of

Al over that needed to form Al over that needed to form feldspar. Muscovite + feldspar. Muscovite + quartz --> andalusite + K-quartz --> andalusite + K-feldspar + water is one feldspar + water is one common reaction.common reaction.

sillimanite

kyanite

andalusite

Cordierite/Cordierite/StauroliteStaurolite

CordieriteCordierite AlAl22(Mg,Fe)(Mg,Fe)22SiSi55AlOAlO18181818

Meta-shales at low pressure, Meta-shales at low pressure, replaced by almandine at high replaced by almandine at high pressure. Looks a bit like pressure. Looks a bit like feldspar. Cyclic twins, inclusions feldspar. Cyclic twins, inclusions and pleochroic haloesand pleochroic haloes

Staurolite Staurolite (Fe,Mg) (Fe,Mg) 22(Al,Fe)(Al,Fe)99OO66(SiO(SiO44)(OH) )(OH) 22

likes Al, Felikes Al, Fe3+3+ and Zn and Zn Meta-shalesMeta-shales

Cyclic twins and a myriad ofInclusions in cordierite

Staurolite porphyroblast

Nepheline - LeuciteNepheline - Leucite

NephelineNepheline NaAlSiONaAlSiO44

Leucite Leucite KAlSi2OKAlSi2O66

The feldspathoids are a silica-poor mineral The feldspathoids are a silica-poor mineral group chemically related to the feldsparsgroup chemically related to the feldspars

Nepheline occurs in silica-deficient alkaline Nepheline occurs in silica-deficient alkaline rocks (gabbros, syenites, basalts, trachytes, rocks (gabbros, syenites, basalts, trachytes, phonolites) and in igneous rocks that have phonolites) and in igneous rocks that have reacted with limestonereacted with limestone

Leucite occurs in K-rich, silica-poor basalts Leucite occurs in K-rich, silica-poor basalts and ultra-mafic lavas. Unstable at moderate and ultra-mafic lavas. Unstable at moderate pressure & does not occur in plutonic rockspressure & does not occur in plutonic rocks

TourmalineTourmaline Tourmaline is an Al-rich Tourmaline is an Al-rich

ferromagnesian mineral that ferromagnesian mineral that contains 10% boron. It occurs in contains 10% boron. It occurs in S-type granites, pegmatites and S-type granites, pegmatites and indeed any rock with boron. Does indeed any rock with boron. Does not ?occur with hornblende.not ?occur with hornblende.

Because it is resistant to abrasion Because it is resistant to abrasion and chemical attack it occurs in and chemical attack it occurs in many sandstones. many sandstones.

Hexagonal with darkest colour with Hexagonal with darkest colour with C-axis normal to polariser.C-axis normal to polariser.

Tourmaline in ppl & xp

CHLORITE CHLORITE (Mg,Al,Fe)(Mg,Al,Fe)1212(Si,Al)(Si,Al)88OO2020(OH) (OH) 1616

Layer silicate that occurs in Layer silicate that occurs in many low-grade many low-grade metamorphic rocks. Also metamorphic rocks. Also occurs as a sub-solidus occurs as a sub-solidus alteration minerals in alteration minerals in igneous rocks (commonly igneous rocks (commonly replacing biotite)replacing biotite)

Chlorite and the clay mineral Chlorite and the clay mineral montmorillonite have very montmorillonite have very similar compositions and on similar compositions and on burial the clay changes to burial the clay changes to chloritechlorite

Titanite CaTi(SiOTitanite CaTi(SiO44)(O,OH,F))(O,OH,F) Titanite (sphene) occurs in many I-type monzonites, Titanite (sphene) occurs in many I-type monzonites,

granodiorites and granites that have magnetite as the Fe/Ti granodiorites and granites that have magnetite as the Fe/Ti oxide (generally have pink K-feldspar)oxide (generally have pink K-feldspar)

Also forms in metamorphic rocks (e.g. meta-basalts) but is Also forms in metamorphic rocks (e.g. meta-basalts) but is not easy to identify when very fine grainednot easy to identify when very fine grained

If Fe-free it is clinozoisite, Never more than one of the three If Fe-free it is clinozoisite, Never more than one of the three Atoms is Fe. Epidote is generally pale yellow in thin sectionAtoms is Fe. Epidote is generally pale yellow in thin section High relief and bright interference colours. In meta-basalts High relief and bright interference colours. In meta-basalts At low and intermediate grade. In altered igneous rocksAt low and intermediate grade. In altered igneous rocks Plagioclase can have fine epidote in the Ca-rich corePlagioclase can have fine epidote in the Ca-rich core In skarns with hedenbergiteIn skarns with hedenbergite Mn epidote called piedmontite is pleochroic (red-black-pink)Mn epidote called piedmontite is pleochroic (red-black-pink)

Epidote: CaEpidote: Ca22(Al,Fe(Al,Fe3+3+))33SiSi33OO1212(OH)(OH)