Information on Polarization Microscopy

M i c r o s c o p y f r o m C a r l Z e i s s

Michel-Lévy Color Chart

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Identification of minerals in polarized light

Polarization in transmitted light

Orthoscopy Conoscopy

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

In orthoscopy, every object point corresponds to a point in the image. Minerals are identified by morphological and optical properties like shape, cracks, color and pleochroism, and by their characteristic in-terference colors. In conoscopy on the other hand, every image point corresponds to a direction in the specimen. This technique requires the use of the highest objective and condenser aper-ture possible.

When the Amici-Bertrand lens is placed in the light path, the interference or axial image in the back focal plane of the speci-men becomes visible. Conoscopy is em-ployed whenever additional information about the specimen is required for optical analysis. It provides interference images that can be seen through the eyepiece and enables differentiation according to 1 or 2 axes and with compensator λ (λ-plate, Red I), according to 1-axis posi-tive/negative or 2-axis positive/negative.

The Phototube Pol is designed for high- performance conoscopy. 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.

2

Eye

Eyepiece

Intermediate image plane

Tube lens

Bertrand lens plane

Intermediate image plane

Bertrand system

DepolarizerAnalyzer

Compensator plane

Objective pupil

Objective

Specimen plane

Condenser

Aperture diaphragm

Polarizer

Luminous field diaphragm

Collector

Light source (filament)

*

* Field of view diaphragm

Inte

rmed

iate

tube

Pol

Determination of birefringence by means of the Michel-Lévy Color Chart

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)

Inserting the lambda compensator(Addition of a path difference of 551 nm) Assumption: second order blue (path difference ca 655 nm)

Effect: In subtraction position the mineral appears lavender- to bluegrey (655 nm – 551 nm = 104 nm)

Rotating the mineral by a further 90°Effect: In this position (addition posi-tion) the mineral appears greenish blue (655 nm + 551 nm = 1206 nm)

Result: The interference color has been identified as a second order blue.

Rotating the mineral into a diagonal position(45° from position of extinction) Maximum brightness Identification of interference color: blue

This amounts to two distinct possibilities: second order blue (path difference ca 655 nm)

third order blue (path difference ca 1150 nm)

Follow the 655 nm line of the path dif-ference across to find the intersection with the corresponding thickness line (usually 25 – 30 μm). From this intersec-tion, follow the "sun line" downwards towards the bottom right to pinpoint

the respective birefringence magnitude on the scale on the right. In this case this leads to a birefringence value of 0.024; the mineral has been identified as an augite.

1

2 43

3

5

Determining the birefringence with the Michel-Lévy Color Chart

-0.040

-0.045

-0.050

-0.055

-0.060

-0.065-0.070

-0.080

-0.090

-0.120

-0.180

200

400

600

800

1000

1200

1400

1600

0 40 97 158

218

234

259

267

275

281

306

332

430

505

536

551

565

575

589

664

728

747

826

843

866

910

948

998

1101

1128

1151

1258

1334

1376

1426

1495

1534

1621

1652

1682

1711

1744

0.00

1

0.00

2

0.00

3

0.00

4

0.00

5

0.00

6

0.00

7

0.00

8

0.00

9

0.01

0

0.01

1

0.01

2

0.01

3

0.01

4

0.01

5

0.01

6

0.01

7

0.01

8

0.01

9

0.02

0

0.02

1

0.02

2

0.02

3

0.02

4

0.02

5

0.02

6

0.02

7

0.02

8

0.02

9

0.03

0

0.03

1

0.03

2

0.03

3

0.03

4

0.03

5

0.03

6

Schwarz Pennin Analcim KryolithLeucit Melilit

EisengrauRipidolit Apophyllit Saponit

Marialit HalloysitLavendelgrau

Philipsit Apatit b-ChristobalitKämmererit Chabazit a-Trikalziumphosphat

GraublauRiebekit Eukolit VesuvianChamosit Vanthoffit Tridymit

Klareres GrauGrünlichweiß Klinozoisit Nephelin SerendibitFast Reinweiß Arfvedsonit Sanidin CoesitGelblichweißBlass Strohgelb Heulandit Beryll OrthoklasStrohgelb Sapphirin Zoisit MicroclinHellgelb Glaserit Harmotom ÅkermanitLebhaft Gelb

Aenigmatit Antigorit Kaolinit

Chrysotil Korund SilicocarnotitBraungelb Triphylit Plagioclas Anorthoclas

An 20-60

Rotorange Topas Albit QuarzEnstatit Cölestin Rankinit

Rot Cordierit Struvit Trikalziumsilikat

Tiefrot Axinit Stilbit GipsPurpur Epistilbit Bronzit BoracitViolett Mg-Riebekit ChrysoberylIndigo

Klinochlor Andalusit GehlenitChloritoid Bytownit Scolecit

HimmelblauLaumontit Natrolith _-DicalciumsilikatHydronephelin Baryt Brushit

Grünlichblau Clintonit Kornerupin PetalitGrün

Dipyr Hypersthen AnorthitStaurolith Thenardit Rhodonit

Margarit Trona

Eckermannit Thuringit Wollastonit

Epidote Jadeit BustamitPicromerit Crossit Boehemit

Helleres Grün Phenakit Monticellit b-DikalziumsilikatGelblichgrün Merwinit Richterit Mullit

Grünlichgelb Syngenit Kyanit GedritNa-Tremolit

Reingelb Hiortdahlit Thomsonit

Orange Lawsonit Pargasit PolyhalitPumpellyit Amesit

Lebhaft Orangerot Melinophan Alunit SpodumenActinolit Vermiculit Amblygonit

Katophorit

Barkevikit Gem. Hornblende BrucitPrehnit Glauberit Gibbsit

Dunkelviolettrot Karpholith Tremolit SillimanitHellbläulichviolett Triplit Hastingsit OrthoferrosilitIndigo

Kainit Pigeonit LarnitOmphacit Gadolinit

Grünlichblau Cookeit Augit Kaersutit

Anthophyllit Turmalin BoraxMeergrün Glaucophan Wavellit Montmorillonit

HydromagnesitGlänzendgrün

Rosenbuschit Wöhlerit CancrinitGrünlichgelb Mizzonit Fassait

Carnallit Titanaugit StishovitFleischfarbe Phlogopit

Karminrot Colemanit Epsomit GlaukonitChloromelanit Paragonit Lepidolit

Babingtonit Salit CalciumhydroxidMattpurpur Hedenbergit

Johannsenit

Violettgrau Högbomit Cummingtonit Pseudowollastonit

Graublau Diopsid Zinnwaldit SucroseClinohumit Dumortierit

MattmeergrünAllanit Chondrodit Lamprophyllit

Bläulichgrün Rhönit Humit ClinoferrosilitPrehnit Forsterit Stilpnomelan

Variscit

Kernit Bischofit

Lazulith Olivin PectolitFe-Epidot

Catapleiit Grandidierit Muscovit

Ana

lcite

Leuc

ite

Apo

phyl

lite

Mar

ialit

e

Apa

tite

Cha

bazi

te

Eudi

alyt

eVa

ntho

ffite

Nep

helin

eSa

nidi

ne

Bery

lZo

isite

Har

mot

ome

Ant

igor

ite

Cor

undu

mPl

agio

clas

eA

n 20

-60

Alb

iteC

eles

tite

Stru

vite

Stilb

iteBr

onzi

teC

hrys

ober

ylA

ndal

usite

Byto

wni

te

Nat

rolit

eBa

rite

Kor

neru

pine

Hyp

erst

hene

Then

ardi

teM

arga

rite

Thur

ingi

te

Jade

iteC

ross

ite

Mon

ticel

lite

Rich

terit

e

Kya

nite

Na-

Trem

olite

Parg

asite

Alu

nite

Verm

icul

iteK

atop

horit

eC

omm

. Hor

nbl.

Gla

uber

ite

Trem

olite

Has

tings

ite

Pige

onite

Om

phac

ite

Aug

ite

Tour

mal

ine

Wav

ellit

eH

ydro

mag

nesi

te

Wöh

lerit

eFa

ssai

te

Tita

naug

itePh

logo

pite

Epso

mite

Para

goni

te

Salit

eH

eden

berg

iteJo

hann

seni

te

Cum

min

gton

ite

Zinn

wal

dite

Cho

ndro

dite

Hum

ite

Fors

terit

eVa

risci

te

Bisc

hofit

e

Oliv

ine

Fe-E

pido

te

Gra

ndid

ierit

e

Penn

ine

Ripi

dolit

e

Phill

ipsi

teK

ämm

erer

ite

Rieb

ecki

teC

ham

osite

Clin

ozoi

site

Arf

veds

onite

Heu

land

iteSa

pphi

rine

Gla

serit

e

Aen

igm

atite

Chr

ysot

ileTr

iphy

lite

Topa

zEn

stat

iteC

ordi

erite

Axi

nite

Epis

tilbi

teM

g-Ri

ebec

kite

Clin

ochl

ore

Chl

orito

id

Laum

ontit

eH

ydro

neph

elite

Clin

toni

te

Dip

yre

Stau

rolit

e

Ecke

rman

nite

Epid

ote

Picr

omer

ite

Phen

akite

Mer

win

ite

Syng

enite

Hio

rtda

hlite

Law

soni

tePu

mpe

llyite

Mel

inop

han

Act

inol

ite

Bark

evik

itePr

ehni

te

Car

phol

iteTr

iplit

e

Kai

nite

Coo

keite

Ant

hoph

yllit

eG

lauc

opha

ne

Rose

nbus

chite

Miz

zoni

te

Car

nalli

te

Col

eman

iteC

hlor

omel

anite

Babi

ngto

nite

Hög

bom

ite

Dio

psid

eC

linoh

umite

Alla

nite

Rhön

ite

Preh

nite

Ker

nite

Lazu

lite

Cat

aple

iite

Cry

olite

Mel

ilite

Sapo

nite

Hal

loys

ite

β-C

risto

balit

eα-

Tric

alci

umph

osph

ate

Vesu

vian

iteTr

idym

ite

Sere

ndib

iteC

oesi

te

Ort

hocl

ase

Mic

rocl

ine

Åke

rman

ite

Kao

linite

Silic

ocar

notit

eA

nort

hocl

ase

Qua

rtz

Rank

inite

Tric

alci

umsi

licat

e

Gyp

sum

Bora

cite

Geh

leni

teSc

olec

ite

γ-D

ical

cium

silic

ate

Brus

hite

Peta

lite

Ano

rthi

teRh

odon

iteTr

ona

Wol

last

onite

Bust

amite

Boeh

mite

β-D

ical

cium

silic

ate

Mul

lite

Ged

rite

Thom

soni

te

Poly

halit

eA

mes

ite

Spod

umen

eA

mbl

ygon

ite

Bruc

iteG

ibbs

ite

Silli

man

iteO

rtho

ferr

osili

te

Larn

iteG

adol

inite

Kae

rsut

ite

Bora

xM

ontm

orill

onite

Can

crin

ite

Stis

hovi

te

Gla

ucon

iteLe

pido

lite

Cal

cium

hydr

oxid

e

Pseu

dow

olla

ston

ite

Sucr

ose

Dum

ortie

rite

Lam

prop

hylli

teC

linof

erro

silit

e

Stilp

nom

elan

e

Pect

olite

Mus

covi

te

Blac

k

Iron

gray

Lave

nder

gra

y

Gra

y bl

ue

Cle

ar g

ray

Gre

enis

h w

hite

Nea

rly p

ure

whi

teYe

llow

ish

whi

tePa

le s

traw

yel

low

Stra

w y

ello

wLi

ght

yello

wBr

ight

yel

low

Brow

n-ye

llow

Red-

oran

ge

Red

Dee

p re

dPu

rple

Vio

let

Indi

go

Sky

blue

Gre

enis

h bl

ueG

reen

Ligh

ter

gree

nYe

llow

ish

gree

n

Gre

enis

h ye

llow

Pure

yel

low

Ora

nge

Brig

ht o

rang

e-re

d

Dar

k vi

olet

-red

Ligh

t bl

uish

vio

let

Indi

go

Gre

enis

h bl

ue

Sea

gree

n

Lust

rous

gre

en

Gre

enis

h ye

llow

Fles

h co

lor

Car

min

e re

d

Dul

l pur

ple

Vio

let-

gray

Gra

y-bl

ue

Dul

l sea

gre

en

Blui

sh g

reen

TephroiteMeioniteAegerine-augiteGruneriteDatolite

TalcMonaziteZirconAegirine

Astrophyllite

Basaltic HornblendeOxyhornblende

AschariteAnatase

Siderophyllite

Baddeleyite

Sphene

BrookiteColumbiteAragoniteCalciteDolomiteMagnesiteSideritePyrophaniteHematiteRutileGeikieliteLepidocrocite

TilleyiteSpurrite

Biotite

Carborundum

Diaspore

Cholesterole

Silk

Nylon

Cellulose

Maltose

Bicalciumferrite

BrownmilleriteGlucose

Carbamide

Monocalciumferrite

LåveniteNontronite

PhengiteTitanbiotiteAnhydrite

PyrophylliteFayaliteIlvaite

Piemontite

Kieserite

Stilpno melane

Cassiterite

Xenotime

Goethite

WhewelliteLudwigite

Path difference [nm](1000nm = 1µm = 10-3mm)

Third OrderSecond OrderFirst Order

Birefringence(nγ – nα)

d [µm]

50

40

30

20

10

0

Thic

knes

s

0,0380,039

0,0410,0430,0440,0450,0470,0480,0490,0500,052

0,055

0,0600,063

0,0650,0700,073

0,080

0,0900,096

0,107

0,1200,1400,1500,1560,1720,1800,1950,2410,2700,2800,2860,360,57

Michel-Lévy Color Chart

4

Read

ing d

irect

ion

linear

linear

biaxial

State of polarization of the light

circularlinear

compensator λ

normal position diagonal position normal position diagonal position

positive

barite

negative

muskovite

0° 45° 90° 135° 180°

Zirc

on

Mu

sco

vite

Spec

imen

State of polarizationof the light

Rotation of the microscope stage

State of polarization of the light

linear circular

compensator λ

without with

without with without with without with without with

without with

circular

uniaxial

positive

quartz

negative

calcite

circular

Linearly and circularly polarized light

Determination of the optical character

Behavior of optically aniso-tropic crystals in linearly and circularly polarized light, orthoscopy and conoscopy.

Determination of the optical character of uniaxial and biaxial minerals in linearly

and circularly polarized light. The reference direction ny of the λ-compensator is aligned in NE-SW.

6

In contrast to linear polarization, circularly polarized light allows minerals to display their interfer-ence colors devoid of extinction. For that reason, circular polariza-tion is the preferred method for image analytical procedures.

Highlights of minerals analysis

7

Mineralogical microscope stand of 1906.

Plagioclase (feldspar) Twin lamination

Pyroxene Cleavage angle ca. 87°

Amphibole Cleavage angle ca. 124°

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.

Carl Zeiss MicroImaging GmbH07740 Jena, Germany

Industrial | Göttingen LocationPhone: + 49 551 5060 660Telefax: + 49 551 5060 464E-Mail: micro@zeiss.de

www.zeiss.de/micro Info

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Kindly supported by TU Bergakademie Freiberg

Dr. M. Magnus Institute of Geology and Paleontology