Microscopy from Carl Zeiss

Michel-Lévy Color Chart

Identification of minerals in polarized light

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Information on Polarization Microscopy Polarization in transmitted light

Orthoscopy Conoscopy

Orthoscopy and conoscopy are the two Eye key methods in traditional transmitted light polarization microscopy. With their different approaches, they provide dif- ferent options, for example for mineral Eyepiece identification in geological microscopy.

The Phototube Pol is designed for high- performance conoscopy. Intermediate image plane Thanks to its additional intermediate image plane with suspended crosshair and field of view diaphragm, it permits the conoscopy of crystals larger than 10 μm.

Tube lens In orthoscopy, every object Bertrand lens plane point corresponds to a point in the image. Minerals are identified by morphological and * optical properties like shape, Intermediate image plane cracks, color and pleochroism, and by their characteristic in- terference colors. In conoscopy Pol tube Intermediate on the other hand, every image Bertrand system point corresponds to a direction Depolarizer in the specimen. This technique Analyzer requires the use of the highest Compensator plane objective and condenser aper- ture possible. Objective pupil Objective When the Amici-Bertrand lens is placed in the light path, the interference or axial image in the back focal plane of the speci- Specimen plane men becomes visible. Conoscopy is em- ployed whenever additional information Condenser about the specimen is required for optical analysis. It provides interference images that can be seen through the eyepiece Aperture diaphragm and enables differentiation according to 1 or 2 axes and with compensator λ Polarizer (λ-plate, Red I), according to 1-axis posi- tive/negative or 2-axis positive/negative. Luminous field diaphragm

Collector

Light source (filament)

2 * Field of view diaphragm Determination of birefringence by means of the Michel-Lévy Color Chart

1

When a ray of light enters an anisotropic medium, it is almost always split into two linearly polarized waves; the ordinary and the extraordinary ray. Both partial rays are characterized by different propagation rates due to different refraction indices. This charac- teristic is called birefringence. The oscillation planes of these two partial rays are perpendicular to each other.

The superposition of the two partial waves (constructive or destruc- tive) is called interference; the colors which appear under crossed (90°) polarizers are called interference colors.

Rotating the mineral into the position of extinction Total extinction (darkest position of mineral)

2 3 4

Rotating the mineral into a diagonal Inserting the lambda compensator Rotating the mineral by a further 90° position (Addition of a path difference of 551 nm) Effect: In this position (addition posi- (45° from position of extinction) Assumption: second order blue tion) the mineral appears greenish blue Maximum brightness (path difference ca 655 nm) (655 nm + 551 nm = 1206 nm) Identification of interference color: blue Effect: In subtraction position the Result: The interference color has been mineral appears lavender- to bluegrey identified as a second order blue. This amounts to two distinct possibilities: (655 nm – 551 nm = 104 nm) second order blue (path difference ca 655 nm) third order blue (path difference ca 1150 nm) 5

Determining the birefringence with the Michel-Lévy Color Chart

Follow the 655 nm line of the path dif- the respective birefringence magnitude ference across to find the intersection on the scale on the right. In this case with the corresponding thickness line this leads to a birefringence value of (usually 25 – 30 μm). From this intersec- 0.024; the mineral has been identified tion, follow the "sun line" downwards as an augite. towards the bottom right to pinpoint

3 Schwarz PenninAnalcim Kryolith Leucit Melilit Eisengrau RipidolitApophyllit Saponit Marialit Halloysit Lavendelgrau PhilipsitApatitb-Christobalit Kämmererit Chabazit a-Trikalziumphosphat Graublau Riebekit Eukolit Vesuvian Chamosit VanthoffitTridymit Klareres Grau GrünlichweißKlinozoisitNephelin Serendibit Fast Reinweiß Arfvedsonit SanidinCoesit Gelblichweiß Blass StrohgelbHeulandit Beryll Orthoklas Strohgelb Sapphirin ZoisitMicroclin Hellgelb Glaserit HarmotomÅkermanit Lebhaft Gelb Aenigmatit Antigorit Kaolinit

ChrysotilKorundSilicocarnotit Braungelb TriphylitPlagioclas Anorthoclas An 20-60

RotorangeTopas AlbitQuarz Enstatit Cölestin Rankinit RotCordierit Struvit Trikalziumsilikat

TiefrotAxinitStilbit Gips PurpurEpistilbitBronzit Boracit ViolettMg-RiebekitChrysoberyl Indigo Klinochlor AndalusitGehlenit ChloritoidBytownit Scolecit Himmelblau LaumontitNatrolith _-Dicalciumsilikat Hydronephelin BarytBrushit GrünlichblauClintonit Kornerupin Petalit Grün DipyrHypersthen Anorthit Staurolith ThenarditRhodonit Margarit Trona oxide osilite

osilite Eckermannit Thuringit Wollastonit notite Michel-Lévy ophyllite ocline ose Epidote Jadeit Bustamit ricalciumphosphate endibite nite ollastonite ona esuvianite -Dicalciumsilicate ridymite ricalciumsilicat e Color Chart Picromerit CrossitBoehemit Cryolite Melilite Saponite Halloysite β -Cristobalite α -T V T Ser Coesite Orthoclase Micr Åkermanite Kaolinite Silicocar Anorthoclase Quartz Rankinite T Gypsum Boracit e Gehlenite Scolecite γ Brushite Petalite Anorthit e Rhodonite Tr W Bustamite Boehmite β -Dicalciumsilicate Mullite Gedrite Thomsonite Polyhalite Amesite Spodumene Amblygonite Brucite Gibbsite Sillimanite Orthoferr Lar Gadolinite Kaersutite Borax Montmorillonite Cancrinite Stishovite Glauconite Lepidolite Calciumhydr Pseudowollastonite Sucr Dumortierite Lampr Clinoferr Stilpnomelane Pectolite Muscovite Helleres Grün PhenakitMonticellitb-Dikalziumsilikat Gelblichgrün Merwinit RichteritMullit nbl.

fite Grünlichgelb Syngenit Kyanit Gedrit odite dite Na-Tremolit emolite omagnesite r olite nerupine 20-60 ossite avellite onzit e emolite anthof ermiculite ariscite itanaugite ourmaline Reingelb Hiortdahlit Thomsonit Analcite Leucite Apophyllite Marialite Apatite Chabazite Eudialyte V Nepheline Sanidine Beryl Zoisite Harmotome Antigorite Corundum Plagioclase An Albite Celestite Struvite Stilbite Br Chrysoberyl Andalusite Bytownite Natr Barit e Kor Hypersthene Thenar Margarite Thuringite Jadeite Cr Monticellite Richterit e Kyanite Na-T Pargasite Alunite V Katophorite Comm. Hor Glauberit e Tr Hastingsite Pigeonite Omphacite Augite T W Hydr Wöhlerite Fassaite T Phlogopite Epsomit e Paragonite Salite Hedenbergite Johannsenite Cummingtonite Zinnwaldite Chondr Humite Forsterite V Bischofite Olivine Fe-Epidote Grandidierite Orange Lawsonit PargasitPolyhalit Pumpellyit Amesit e erite Lebhaft Orangerot Melinophan Alunit Spodumen omelanite e olite onephelit e

dierite ActinolitVermiculit Amblygonit nallite omerit e nite

ehnite ehnite Katophorit riphylit e riplite opaz Pennine Ripidolit e Phillipsite Kämmer Riebeckite Chamosite Clinozoisite Arfvedsonite Heulandite Sapphirine Glaserite Aenigmatite Chrysotile T T Enstatite Cor Axinite Epistilbite Mg-Riebeckite Clinochlor Chloritoid Laumontite Hydr Clintonite Dipyr Staur Eckermannite Epidote Picr Phenakit e Merwinite Syngenite Hiortdahlite Lawsonite Pumpellyite Melinophan Actinolite Barkevikite Pr Carpholite T Kainite Cookeite Anthophyllite Glaucophane Rosenbuschit e Mizzonite Car Colemanit e Chlor Babingtonite Högbomite Diopside Clinohumit e Allanite Rhönite Pr Ker Lazulite Catapleiite BarkevikitGem. Hornblende Brucit Birefringence Prehnit Glauberit Gibbsit (nγ – nα) 0.020 0.019 0.018 0.012 0.002 0.014 0.001 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.010 0.011 0.013 0.015 0.016 0.017 0.030 0.021 0.022 0.023 0.024 0.025 0.026 0.027 0.028 0.029 0.031 0.032 0.033 0.034 0.035 0.036 DunkelviolettrotKarpholithTremolitSillimanit HellbläulichviolettTriplit Hastingsit Orthoferrosilit d [µm] Indigo Kainit Pigeonit Larnit Omphacit Gadolinit

GrünlichblauCookeitAugit Kaersutit

AnthophyllitTurmalinBorax 50 Meergrün Glaucophan Wavellit Montmorillonit Hydromagnesit Glänzendgrün

Thickness -0.040 Tephroite Tilleyite Låvenite 0,038 RosenbuschitWöhlerit Cancrinit Meionite Spurrite Nontronite 0,039 GrünlichgelbMizzonit Fassait Aegerine- Biotite CarnallitTitanaugit Stishovit augite Phengite 0,041 Fleischfarbe Phlogopit Titanbiotite 0,043 40 -0.045 Grunerite Datolite Anhydrite 0,044 Karminrot Colemanit EpsomitGlaukonit Carborundum 0,045 Chloromelanit Paragonit Lepidolit Talc Pyrophyllite 0,047 -0.050 Monazite Diaspore Fayalite 0,048 Babingtonit SalitCalciumhydroxid Zircon Ilvaite 0,049 MattpurpurHedenbergit Aegirine Cholesterole 0,050 Johannsenit -0.055 Astrophyllite 0,052 ViolettgrauHögbomitCummingtonit Pseudowollastonit 30 Silk Piemontite 0,055 -0.060 Graublau DiopsidZinnwalditSucrose Nylon 0,060 Clinohumit Dumortierit -0.065 Basaltic Hornblende Kieserite 0,063 Mattmeergrün -0.070 Oxyhornblende AllanitChondrodit Lamprophyllit Cellulose 0,065 BläulichgrünRhönitHumit Clinoferrosilit Ascharite 0,070 Prehnit Forsterit Stilpnomelan -0.080 Anatase Maltose 0,073 Variscit Siderophyllite Stilpno melane 0,080 Kernit Bischofit 20 -0.090 Bicalciumferrite Brownmillerite 0,090 Lazulith Olivin Pectolit Fe-Epidot Glucose Cassiterite 0,096 Catapleiit Grandidierit Muscovit -0.120 Baddeleyite Xenotime 0,107 Sphene Carbamide 0,120 Brookite Goethite 0,140 -0.180 Columbite Monocalciumferrite 0,150 10 Aragonite Whewellite 0,156 Calcite Ludwigite 0,172 Dolomite 0,180 Magnesite 0,195 Siderite 0,241 Pyrophanite 0,270 Hematite 0,280 Rutile 0,286 Geikielite 0,36 0 Lepidocrocite 0,57 Reading direction Reading

0 Path difference [nm] 97 40 -3 72 8 74 7 82 6 84 3 86 6 91 0 94 8 99 8 50 5 53 6 55 1 56 5 57 5 58 9 66 4 43 0 25 9 33 2 26 7 30 6 27 5 28 1 15 8 21 8 23 4 (1000nm = 1µm = 10 mm) 1711 1621 1652 1682 1744 1258 1334 1376 1426 1495 1534 1101 1128 1151 400 600 800 200 100 0 120 0 140 0 160 0 ed een d een een e whit een een d een ous gr e yellow eenish blue eenish yello w eenish yello w eenish whit e eenish blue een own-yellow on gray Orange d Bright orange- re Dark violet-r Light bluish violet Indigo Gr Sea gr Lustr Gr Flesh color Carmine re Dull purple Violet-gra y Gray-blue Dull sea gr Bluish gr Gr Pur 4 Blac k Ir Lavender gray Gray blue Clear gray Gr Nearly pur llowish whit e Ye Pale straw yellow Straw yello w Light yello w Bright yello w Br Red-orange Red Deep re Purpl e Violet Indigo Sky blue Gr Gr Lighter gr llowish gr Ye

First Order Second Order Third Order Linearly and circularly polarized light

State of polarization Rotation of the microscope stage In contrast to linear polarization, of the light 0° 45° 90° 135° 180° circularly polarized light allows minerals to display their interfer- ence colors devoid of extinction. For that reason, circular polariza- linear tion is the preferred method for

n image analytical procedures. Zirco

circular

Behavior of optically aniso-

Specimen tropic crystals in linearly and linear circularly polarized light,

te orthoscopy and conoscopy. Muscovi circular

Determination of the optical character

State of polarization of the light linear circular uniaxial compensator λ without with without with

Determination of the optical positive character of uniaxial and quartz biaxial minerals in linearly and circularly polarized light. The reference direction ny of the λ-compensator is aligned negative in NE-SW. calcite

State of polarization of the light linear circular

biaxial compensator λ without with without with without with without with normal position diagonal position normal position diagonal position

positive barite

negative muskovite

6 Highlights of minerals analysis

Auguste Michel-Lévy (1844 –1911) French geologist, Inspector General of Mining and director of the Geological Survey in France, made a name for himself by his research into extrusive rocks, their microscopic structure and origin.

Until this day, the interference color chart proposed by him in 1888 remains an important tool in the identi- fication of thin sections of minerals with polarization microscopy.

Then as now, Carl Zeiss sets benchmarks with their polarized light microscopes, in mineralogy and petrography as well as materialography and other application fields.

Mineralogical microscope stand of 1906.

Plagioclase (feldspar) Pyroxene Amphibole Twin lamination Cleavage angle ca. 87° Cleavage angle ca. 124°

7 Kindly supported by TU Bergakademie Freiberg

Dr. M. Magnus Institute of Geology and Paleontology

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www.zeiss.de/micro Information subject to change. Printed on environmentally friendly paper bleached without cholorine. 70-2-0100/e – printed 02.2011