Introduction toIntroduction toIntroduction to Introduction to the optical the optical pp

microscopy of microscopy of mineral mineral fibresfibres

Don Halterman, United States of AmericaDon Halterman, United States of America

Official DisclaimerOfficial DisclaimerOfficial DisclaimerOfficial Disclaimer

I am employed by the United States Department of LaborI am employed by the United States Department of LaborI am employed by the United States Department of Labor I am employed by the United States Department of Labor (DOL) Occupational Safety and Health Administration (DOL) Occupational Safety and Health Administration (OSHA), Salt Lake Technical Center, Industrial Hygiene and(OSHA), Salt Lake Technical Center, Industrial Hygiene and(OSHA), Salt Lake Technical Center, Industrial Hygiene and (OSHA), Salt Lake Technical Center, Industrial Hygiene and Chemistry Laboratory. I also provide asbestos analysis for Chemistry Laboratory. I also provide asbestos analysis for the Mine Safety and Health Administration (MSHA).the Mine Safety and Health Administration (MSHA).

This presentation is my own, and does not constitute an This presentation is my own, and does not constitute an p y ,p y ,official statement by OSHA. All opinions expressed are my official statement by OSHA. All opinions expressed are my own, and do not represent official statements of policy or own, and do not represent official statements of policy or b l t b db l t b dbear any regulatory burden. bear any regulatory burden.

Return to mineralogy classReturn to mineralogy classReturn to mineralogy class . . .Return to mineralogy class . . .

What we will study:What we will study:What we will study:What we will study:

••History of polarized light microscopy (PLM)History of polarized light microscopy (PLM)••Advantages of PLMAdvantages of PLM••Advantages of PLMAdvantages of PLM••Disadvantages of PLMDisadvantages of PLM••Understanding the microscopeUnderstanding the microscopeAnalyzingAnalyzing fibresfibres••Analyzing Analyzing fibresfibres

History of PLM in mineralogyHistory of PLM in mineralogyHistory of PLM in mineralogyHistory of PLM in mineralogyThe history of the PLM is theThe history of the PLM is theThe history of the PLM is the The history of the PLM is the

history of mineralogyhistory of mineralogy

JJ M d iM d iR é J tR é J t H üH ü Joe Joe MandarinoMandarinoRené Just René Just HaüyHaüy

Walter Walter McCroneMcCrone

Is PLM obsolete?Is PLM obsolete?Is PLM obsolete?Is PLM obsolete?•• Original work on crystallographyOriginal work on crystallography•• Original work on crystallography, Original work on crystallography,

optical crystallography, and optical optical crystallography, and optical properties were done with theproperties were done with theproperties were done with the properties were done with the microscopemicroscope

•• Some tests can still only beSome tests can still only be•• Some tests can still only be Some tests can still only be performed with the microscopeperformed with the microscope

•• With the correct equipment andWith the correct equipment and•• With the correct equipment and With the correct equipment and knowledge, the PLM can tell us many knowledge, the PLM can tell us many things other instruments cannotthings other instruments cannotthings other instruments cannotthings other instruments cannot

Technical advantages of PLMTechnical advantages of PLMgg•• Can determine many different properties with Can determine many different properties with

one toolone tool•• Refractive index, optic sign, anisotropy, basic Refractive index, optic sign, anisotropy, basic p g pyp g py

structure, crystal system, growth & breakage habits, structure, crystal system, growth & breakage habits, textures, and moretextures, and more

PLM: value for the moneyPLM: value for the moneyyyGood quality PLM Good quality PLM

with basicwith basic Or buy from eBay: Or buy from eBay: $3 000 t $6 000$3 000 t $6 000

Can take to the Can take to the fi ld ith b ttfi ld ith b ttwith basic with basic

accessories: accessories: $12,000 to $20,000 $12,000 to $20,000

USDUSD

$3,000 to $6,000 $3,000 to $6,000 USDUSD

field with battery field with battery power!power!

PLM: some challengesPLM: some challengesgg

Disadvantage: cannot see small particles lessDisadvantage: cannot see small particles less•• Disadvantage: cannot see small particles less Disadvantage: cannot see small particles less than ~ 0.2 µm in diameter (with phase contrast than ~ 0.2 µm in diameter (with phase contrast PLM)PLM)PLM)PLM)•• Solution: use SEM as an Solution: use SEM as an auxillaryauxillary methodmethod

•• A very useful tool, but sometimes the results are A very useful tool, but sometimes the results are ambiguousambiguous•• Use XRD, SEM with EDS, or TEM with SAED as Use XRD, SEM with EDS, or TEM with SAED as

supplemental methodssupplemental methods

Versus other instruments . . Versus other instruments . . ..

•• XX--ray ray diffractometerdiffractometer: ~$250,000: ~$250,000•• Crystal structure, but not Crystal structure, but not habithabit!!

•• SEM w/EDS: ~$200,000SEM w/EDS: ~$200,000•• Habit, chemistryHabit, chemistry•• Supplement to PLMSupplement to PLM

Versus other instruments . . Versus other instruments . . ..

•• TEM w/SAED: ~$1,000,000TEM w/SAED: ~$1,000,000•• Difficult to determine fibrous Difficult to determine fibrous

habit; bias toward small habit; bias toward small ti l i & diffi ltti l i & diffi ltparticles; expensive & difficultparticles; expensive & difficult

The special effects of light are always presentThe special effects of light are always present

The phenomena of light are all around us. Only in special The phenomena of light are all around us. Only in special circumstances do we witness diffraction refractioncircumstances do we witness diffraction refractioncircumstances do we witness diffraction, refraction, circumstances do we witness diffraction, refraction, dispersion, and other effects with the naked eye. To see dispersion, and other effects with the naked eye. To see these effects on demand we must use the microscope andthese effects on demand we must use the microscope andthese effects on demand, we must use the microscope and these effects on demand, we must use the microscope and certain filters to isolate and amplify the phenomena.certain filters to isolate and amplify the phenomena.

Let there be lightLet there be lightLet there be lightLet there be light

“Li ht i ti“Li ht i ti i l t ti fi ldi l t ti fi ld“Light is a time“Light is a time--varying electromagnetic field varying electromagnetic field that vibrates perpendicular to its propagation that vibrates perpendicular to its propagation direction, with the electric and magnetic direction, with the electric and magnetic components vibrating perpendicular to eachcomponents vibrating perpendicular to eachcomponents vibrating perpendicular to each components vibrating perpendicular to each other. For the purposes of analyzing visible other. For the purposes of analyzing visible light the magnetic vector can be ignored Inlight the magnetic vector can be ignored Inlight, the magnetic vector can be ignored. In light, the magnetic vector can be ignored. In microscopy, we are concerned with the wave microscopy, we are concerned with the wave nature of light, not the photonic nature of light.”nature of light, not the photonic nature of light.”

Ride the wavesRide the wavesRide the wavesRide the waves

Privileged light: polarizationPrivileged light: polarizationPrivileged light: polarizationPrivileged light: polarization

A linear polarizer only allows light to pass in one directionA linear polarizer only allows light to pass in one directionA linear polarizer only allows light to pass in one direction A linear polarizer only allows light to pass in one direction of vibration. This is called the “privileged direction.” of vibration. This is called the “privileged direction.”

Crossed polarizers: you shall not passCrossed polarizers: you shall not passCrossed polarizers: you shall not passCrossed polarizers: you shall not pass

If another linear polarizer is placed after the first polarizerIf another linear polarizer is placed after the first polarizerIf another linear polarizer is placed after the first polarizer, If another linear polarizer is placed after the first polarizer, with the privileged direction set 90 degrees to the first with the privileged direction set 90 degrees to the first polarizer then the polarized light cannot pass andpolarizer then the polarized light cannot pass andpolarizer, then the polarized light cannot pass, and polarizer, then the polarized light cannot pass, and extinction occurs. extinction occurs.

The colors of interferenceThe colors of interferenceIf a birefringent (anisotropic) crystalline material is placed between If a birefringent (anisotropic) crystalline material is placed between th d l i th li ht i lit i t t hi h thth d l i th li ht i lit i t t hi h ththe crossed polarizers, the light is split into two rays, which then the crossed polarizers, the light is split into two rays, which then recombine. The mathematical effect of the recombined waves is recombine. The mathematical effect of the recombined waves is perceived as a color by our eyesperceived as a color by our eyesperceived as a color by our eyes.perceived as a color by our eyes.

These colors do not occur with These colors do not occur with h i t i t i lh i t i t i lamorphous or isotropic materialsamorphous or isotropic materials

Fibrous glassFibrous glass Halite fluorite etcHalite fluorite etc –– isometricisometricFibrous glass Fibrous glass ––amorphousamorphous

Halite, fluorite, etc. Halite, fluorite, etc. –– isometric isometric system. No birefringencesystem. No birefringence

Example on the macro scaleExample on the macro scaleExample on the macro scaleExample on the macro scale

““polariscopepolariscope” ” with crossedwith crossed

Muscovite mica, Muscovite mica, hand samplehand sample

Crossed polarizers Crossed polarizers with sensitive tintwith sensitive tintwith crossed with crossed

polarizerspolarizershand samplehand sample with sensitive tint with sensitive tint

plate, light onplate, light on

Example on the macro scaleExample on the macro scaleExample on the macro scaleExample on the macro scale

M sco ite micaM sco ite mica MaximumMaximumMuscovite mica Muscovite mica Maximum Maximum retardationretardation

We will discuss extinction, retardation We will discuss extinction, retardation l d ti i i th l b tl d ti i i th l b tcolors, and optic sign in the laboratorycolors, and optic sign in the laboratory

Refraction: Snell’s Law and bending lightRefraction: Snell’s Law and bending lightRefraction: Snell s Law and bending lightRefraction: Snell s Law and bending light

Wh li ht t t tWh li ht t t t••When a light wave enters a transparent When a light wave enters a transparent material perpendicular to the surface, it is material perpendicular to the surface, it is p pp pslowed down (retarded) but not refracted.slowed down (retarded) but not refracted.

••When a light wave enters a material at anWhen a light wave enters a material at an••When a light wave enters a material at an When a light wave enters a material at an angle, the light is bent, or refracted, angle, the light is bent, or refracted, according toaccording to Snell’s LawSnell’s Lawaccording toaccording to Snell’s LawSnell’s Law. .

Refraction: Snell’s Law and bending lightRefraction: Snell’s Law and bending lightRefraction: Snell s Law and bending lightRefraction: Snell s Law and bending light

Refractive index (RI)Refractive index (RI)

Snell’s Law: important factsSnell’s Law: important factsSnell s Law: important factsSnell s Law: important facts

The index of refraction is different forThe index of refraction is different for•• The index of refraction is different for The index of refraction is different for every wavelength of light. This is every wavelength of light. This is dispersiondispersion Every material has aEvery material has adispersiondispersion. Every material has a . Every material has a different coefficient of dispersion.different coefficient of dispersion.

•• When light enters and leaves materials of When light enters and leaves materials of different RI, it refracts toward the medium with different RI, it refracts toward the medium with the higher RI When there is no change there isthe higher RI When there is no change there isthe higher RI. When there is no change, there is the higher RI. When there is no change, there is no refraction at the interface of the two media. no refraction at the interface of the two media. This is how we measure RI by “the immersion This is how we measure RI by “the immersion

th d ” ( t lid )th d ” ( t lid )method.” (next slide)method.” (next slide)

Snell’s Law: important factsSnell’s Law: important factsSnell s Law: important factsSnell s Law: important facts

How do we use these principles to How do we use these principles to recognize regulated bulk asbestos?recognize regulated bulk asbestos?

• A technique called “dispersion staining”• This is an optical phenomenon, no “stain” is applied to

the sample!• Optical dispersion staining was known for years;

d l b F D ld Bl W lt M Cmade popular by F. Donald Bloss, Walter McCrone, and Su-Chun Su

• Walter McCrone showed a specific RI immersion liquid for each of the six regulated asbestos types that will cause dispersion colors to be seenthat will cause dispersion colors to be seen

How does dispersion staining work?How does dispersion staining work?o does d spe s o sta g oo does d spe s o sta g o

• The sample must be immersed in RI liquid• The sample must be immersed in RI liquid• Both the mineral and the RI liquid must have

l th i th i ibl f li ht fone wavelength in the visible range of light for which they share the same refractive index

• By blocking out this common wavelength with a “central stop objective,” we see the p j ,complementary dispersed colors at the edges of the crystal, and these are “dispersion y , pcolors”

A tasteA taste ofavageofavageA taste A taste ofavageofavage

The test protocolThe test protocolThe test protocolThe test protocol•• Bulk asbestos analysts learn to follow a Bulk asbestos analysts learn to follow a

series of easy testsseries of easy tests•• These tests use specific RI liquids for These tests use specific RI liquids for

specific asbestos typesspecific asbestos typesspecific asbestos typesspecific asbestos types•• Very few other materials exhibit dispersion Very few other materials exhibit dispersion

colors in these liquidscolors in these liquidscolors in these liquidscolors in these liquids

Amosite in HD 1.670Amosite in HD 1.670 Chrysotile Chrysotile HD 1 550HD 1 550

anthophylliteanthophyllite

HD 1.550HD 1.550

Quick testing recipe for six commercial Quick testing recipe for six commercial g pg pasbestos speciesasbestos species

•• chrysotile, 1.550chrysotile, 1.550•• amosite 1 670 or 1 680amosite 1 670 or 1 680•• amosite, 1.670 or 1.680amosite, 1.670 or 1.680•• crocidolite, 1.680crocidolite, 1.680•• anthophyllite 1 620anthophyllite 1 620•• anthophyllite, 1.620anthophyllite, 1.620•• tremolite, 1.620tremolite, 1.620

ti litti lit 1 6401 640•• actinoliteactinolite, 1.640, 1.640•• talc, 1.605 talc, 1.605 –– talc is not colored, anthophyllite will have talc is not colored, anthophyllite will have

colorscolorscolorscolors

PleochroismPleochroism

C id li (C id li ( bl ) d ibl ) d i•• Crocidolite (grayCrocidolite (gray--blue) and amosite blue) and amosite (brown) have strong colors(brown) have strong colors( ) g( ) g

•• You can see these colors under the You can see these colors under the microscope in planemicroscope in plane polarized lightpolarized lightmicroscope in planemicroscope in plane--polarized lightpolarized light

•• The colors change when the fiber is The colors change when the fiber is parallel or perpendicular to the polarizer parallel or perpendicular to the polarizer

crocidolitecrocidolitecrocidolitecrocidolite

amositeamositeamositeamosite

SummarySummarySummarySummaryWe will We will

• Only the “federal the asbestos standards 1910.1001(b), 1926.1101, & 1915.1001( ), ,

• (e.g., winchite, erionite are not)• Altered., acid-washed or heated chrysotile)Altered., acid washed or heated chrysotile)• Cleavage regulated

What do a “What do a “fibrefibre” cont’d” cont’dWhat do a What do a fibrefibre … cont d … cont d

•• A regulated >= 5 µm long with >= 3:1 (OSHA IDA regulated >= 5 µm long with >= 3:1 (OSHA ID--160)160)

•• FibresFibres that are plant that are plant fibrefibre, fibrous glass, synthetic , fibrous glass, synthetic b esb es t at a e p a tt at a e p a t b eb e, b ous g ass, sy t et c, b ous g ass, sy t et cfibrefibre, etc.), etc.)

What do a “What do a “fibrefibre” cont’d” cont’dWhat do a What do a fibrefibre … cont d … cont d

CC•• Caveats:Caveats:

11 Asbestos USA differentAsbestos USA different defintionsdefintions forfor1.1. Asbestos USA, different Asbestos USA, different defintionsdefintions for, for, 2.2. And best of for the definition of a And best of for the definition of a fibrefibre . . . . . .

Therefore . . .Therefore . . .

Who e?Who e?All with a >=3:1 aspect them)All with a >=3:1 aspect them)))

Is there a unique?Is there a unique?Is there a unique?Is there a unique?

NN T t ll C th i SkiT t ll C th i Ski•• No. No. To quote my colleague Catherine Skinner, To quote my colleague Catherine Skinner, “although it is a“although it is a

Final thoughts and philosophyFinal thoughts and philosophyFinal thoughts and philosophyFinal thoughts and philosophy

Wh i it ?Wh i it ?•• Why is it so?Why is it so?

•• “We regulate not make people sick.” “We regulate not make people sick.” –– Daniel T. Daniel T. Crane, I am effects. “ Crane, I am effects. “

Thank you for listening!Thank you for listening!Thank you for listening!Thank you for listening!

Grazie danke sehr Je vous remercieGrazie, danke sehr, Je vous remercie, dank je, hvala ti, gracias, ευχαριστώ,

б l t kkü d icпасибо, mul umesc, teşekkür ederim, etc.