Biaxial Minerals Descriptions

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1 Bixil Minerls Desriptions Olivine Pyroxenes Orthopyroxene Clinopyroxene Amphiole Hornlende Atinolite Mis Biotite, musovite, hlorite Feldsprs Plgiolse Miroline, ortholse, snidine Feldsprs Tetosilites -Si:O= 1:2 Most undnt group of minerls. Found in igneous, metmorphi nd sedimentry roks Two groups of feldspr: 1. Alkli Feldsprs ortholse ] miroline ] KAlSi 3 O 8 snidine ] Eh of these polymorphs re stle t different tempertures. 2. Plgiolse Feldspr - vrile ompositions NAlSi 3 O 8 - CAl 2 Si 2 O 8 - NiSi = CAl Alite Anorthite Generl Formul (N,C)Al(Al,Si)Si 2 O 8 Plgiolse Feldsprs Mixture of Alite (N-rih) nd Anorthite (C-rih). % A % An Alite Oligolse Andesine Lrdorite Bytownite Anorthite All re trilini, with low symmetry, inditrix nd rystllogrphi xes do not oinide 1

2 W-E '59, Revised '78, G.F., Brok Univ () () () (d) (e) (f) (g) Vritions in the opti orienttion of the giolse feldsprs with omposition: () high-lite, () low-lite, () oligolse, (d) ndesine, (e) lrdortie, (f) ytownite, (g) northite. Note how the position of the opti xil ne moves with inresing An ontent. Plgiolse R.I. A An n α = n β = n γ = vrition with omposition (figure 15.6, p. 262) Low relief Low irefringene - mximum 1 st order grey or white 2V ngle vries from 45 to 2, +ve or -ve with vrying omposition Colourless in thin setion; non eohroi my e loudy in ne light due to ltertion to seriite. Extintion Angle n 50 Qurtz ε RI n ω OPTIC ANGLE (2V) n γ n β n α Mximum Extintion in zone to () () () () Setions Setions Bx () o Bx () Refrtive Index (n) Plgiolse Physil nd optil properties vry with omposition Composition of Plgiolse n e determined to within < 5% An y mesuring extintion ngles whih reflet vritions in the optil properties due to vritions in omposition. 50 Setions A An Mol. % An Alite Oligolse Andesine Lrdorite Bytownite Anorthite 2

Plgiolse Clevge 1 perfet levge to 1 good levge to interset t 93-94 levges ontrol frgment shpe nd orienttion Plgiolse levge is est visile with the perture diphrgm stopped down to

3 Plgiolse Clevge 1 perfet levge to 1 good levge to interset t levges ontrol frgment shpe nd orienttion Plgiolse levge is est visile with the perture diphrgm stopped down to emphsize the little relief present. glue px G.C. Finn, 05 px Plgiolse Twinning is hrteristi of giolse. sent in smll grins, prtiulrly in metmorphi roks px px px px opx px From D. Shulze, 04 3

Periline h01 omposition ne, polysyntheti, twofold rottion out xis, 3.

4 Plgiolse Twins re sed on vrious twin lws Common twin lws re: 1. Alite omposition ne, polysyntheti or repeted twinning (these re the twins visile s stritions in hnd sme of giolse) 2. Periline h01 omposition ne, polysyntheti, twofold rottion out xis, 3. Crlsd omposition ne, penetrtion twin, twofold rottion out xis Alite twinning oserved in ll ompositions, periline nd Crlsd in intermedite nd li giolse (An-rih). Polysyntheti Twin Consists of numerous twin segments joined on prllel twin nes Alite Twin Plne ( ne) G.C. Finn, 05 Polysyntheti Twin Consists of numerous twin segments joined on prllel twin nes Periline Twins Alite Twins From: 4

Contt Twins Joined y smooth twin ne seprting the segments Crlsd-lite Twin Plne G.C. Finn, 05 Plgiolse 0 setion, to xis In PPL - 2 levges not t 90 In PL - lite nd periline twins

5 Contt Twins Joined y smooth twin ne seprting the segments Crlsd-lite Twin Plne G.C. Finn, 05 Plgiolse 0 setion, to xis In PPL - 2 levges not t 90 In PL - lite nd periline twins Crystllogrphi Orienttion PL PPL Plgiolse 0 setion, to xis Alite twins re length fst Periilne twins re length slow (Fst Ry) (Slow Ry) Opti Orienttion Cn mesure two extintion ngles: ^ ^ PL PPL 5

Plgiolse setion, to xis In PPL - 1 levge to In PL - periline twins/zoning Crystllogrphi Orienttion Plgiolse setion, to xis Periline twins, to, re length fst Alite twins not visile (Fst Ry) (Slow Ry)

6 Plgiolse setion, to xis In PPL - 1 levge to In PL - periline twins/zoning Crystllogrphi Orienttion Plgiolse setion, to xis Periline twins, to, re length fst Alite twins not visile (Fst Ry) (Slow Ry) Opti Orienttion Cn mesure extintion ngle: ^ Eh zone will hve seprte extintion ngle Anomlous Extintion Chemil ontion Optil properties vry with hemil omposition, resulting in vrying extintion diretions for minerl eg. zoned minerls like giolse nd olivine From D. Shulze, 04 6

7 W-E '59, Revised '78, G.F., Brok Univ Crystllogrphi Orienttion/Opti Orienttion Cn mesure extintion ngle: ^ Plgiolse setion, to xis In PPL - 1 levge to In PL lite (fst) nd periline (slow) (Fst Ry) twins (Slow Ry) Plgiolse Optil orienttion vries on regulr sis with omposition nd provides mens of determining ompositions (Do in Petrology) Distinguishing Fetures low relief olourless ixil twinning Extintion Angle n 50 Qurtz ε RI n ω OPTIC ANGLE (2V) n γ n β n α Mximum Extintion in zone to () () () () Setions Setions Bx () o Bx () Refrtive Index (n) Plgiolse Physil nd optil properties vry with omposition Composition of Plgiolse n e determined to within < 5% An y mesuring extintion ngles whih reflet vritions in the optil properties due to vritions in omposition. 50 Setions A An Mol. % An Alite Oligolse Andesine Lrdorite Bytownite Anorthite 7

Biaxial Minerals Descriptions

Biaxial Minerals Descriptions Biaxial Minerals Desriptions Olivine Pyroxenes Orthopyroxene Clinopyroxene Amphiole Atinolite Mias Biotite, musovite, hlorite Feldspars Plagiolase Miroline, ortholase, sanidine Amphioles Two groups to