How to Make a Thin Section
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Transcript of How to Make a Thin Section
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How to make a thin section
Dave's methods at WWU Geology
Note: this document is online at www.davehirsch.com (under "Miscellany")
What is a thin section?
A thin section is a 30 m (= 0.03 mm) thick slice of rock attached to a glass slide with epoxy.
Typical thin section slides are 2 mm x ! mm" altho#gh larger ones can $e prod#ced. They are
generally co%ered $y another glass slide" a co%er slip also attached to the rock with epoxy. Theepoxy ideally has an index of refraction of &.'!" altho#gh o#r epoxy is slightly higher" perhaps
&.'.
The sections may $e left #nco%ered for chemical analysis on the * or electron micropro$e. +f
so" temporary co%er slips may $e weakly attached with glycerin.
Thin section making equipment
There are fi%e main tools yo# will #se, The sla$ saw" the trim saw" the grinder" the c#t-off saw"
and the lap wheels. o# will want a harpie-type permanent marker" some li/#id paper and afine-tipped permanent marker.
arnings, Things yo# can damage in the la$
1e s#re when yo# #se either the c#t-off saw" or the thin section grinder" that the $ottle is
less than half f#ll of water. +f it gets too f#ll" water can $e s#cked into the $#ildings%ac##m system. This wo#ld $e $ad. ont do this.
1e s#re to clean and dry the grinding wheels promptly after yo# finish #sing each one" or
they will r#st rapidly. +nstr#ctions for this are gi%en $elow.
1e s#re to #se the correct grit for each grinding wheel. 4rom left to right" they get finer
and the grit n#m$ers get larger, &20" 2!0" !00" 00.
Making your thin section
(5ote, yo# can click any image for a greatly-
enlarged %ersion)
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This g#ide is descri$ed in steps" withphotos of a sample rock shown alongside
as it #ndergoes the %ario#s steps.
tep 6ne7, 8repare the glass slide
7o# dont act#ally ha%e to do this first. +n fact" + often do this for awhole $#nch of slides at once" then #se them as needed.
The glass slide yo# will gl#e the rock to
m#st $e flat in order for the rock sectionto end #p with a constant thickness. +n
order to achie%e this yo# need to 9frost9
the slide" which accomplishes two goals,
&. :emo%es the thick spots on theslide
2. Ad;#sts the slide face to $e parallel
to the grinding wheels face.
To do this s#ccessf#lly" yo# need to $ea$le to keep the slide in the same
orientation $oth which yo# are frosting it
and later when yo# are grinding it. +
accomplish this $y grinding off a cornerof the slide #sing the 2!0 grit grinding
wheel.
rinding
wheels. heels ha%e
partic#lar a$rasi%es,
rightmost wheel is &20
grit" then 2!0 grit(open)" then !00 grit"
then 00 grit . >lassslide corners are
gro#nd #sing the 2!0
grit wheel.
4ig#re 2. 8#tting wateron spinning wheel.
4ig#re 3. 8#tting 2!0-
grit a$rasi%e on
spinning" wet wheel.
4ig#re !. >rinding the
corner of a glass slide
on the wheel.
4ig#re '. >lass slidewith a corner gro#nd
off. 5ote reflection -
its not yet frosted.
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wheel (if yo# #se the right side"which is mo%ing towards yo#" it
may kick o#t of yo#r hand).
'. 6nce a small amo#nt has gro#ndaway" yo#re done. lean allgrit
off the slide in the sink.
. o# m#st clean the wheel
promptly" or it will r#st. The nextsection descri$es how.
leaning the grinding wheel
o# m#st clean the grinding wheelspromptly" or they will r#st. . ry the spinning wheel with thehair dryer #ntil its totaly dry.
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+. lean the $ench top that holds thewheels.
tep Two, 4rost the glass slide
o# will now 9frost9 or grind the glass
slide to flatten it o#t and ro#ghen the
s#rface so the epoxy can $ind well. Toaccomplish this" yo# m#st always place
the slide on the grinder in the same
orientation. (+ always p#t the slide on so
that the c#t-off corner points #p andtowards me).
&. T#rn on the water to the grinder.
2. 4ind a fairly clean slide (not
frosted) and place it on the slideholder of the c#t-off saw (wet it if
it doesnt stick). This is $eca#se
the two de%ices share a %ac##msystem" and the one not in #se
m#st ha%e a slide to create a seal.
3. ipe clean the slide holder of the
grinder. Any grit will prod#cescratches on the finished section.
!. 8lace the section on the holder of
the grinder.
'. T#rn on the %ac##m (the %al%e is$etween the two instr#mentsB its
on when it points away from the
wall). heck to see that the slide is
firmly held.
. T#rn the control towards yo# #ntil
it reads a$o#t ?0. (This is co#nter-
clockwiseB yo# sho#ld see the left
part of the grinder mo%e awayfrom the right part which holds the
4ig#re &0. #t-off saw
(left) and thin section
grinder (right). 5ote
that water controls are$etween sink and c#t-
off saw" and %ac##mcontrols are $etweenthe two.
4ig#re &&. lide on
grinder showingposition incl#ding
gro#nd corner.
4ig#re &2. 8lacing
slide on grinder for
frosting. 1e s#re slide
rests against the pins"and place it on the
holder with the
%ac##m t#rned off.
4ig#re &3. >rinder
control with n#mericalga#ge.
4ig#re &!. lidemostly frosted" $#t
with #nfrosted portion
at top.
4ig#re &'. lide
completely frosted.
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grinding wheel).
?. T#rn on the motor.
@. hile mo%ing the slide $ack andforth" slowly t#rn the control
clockwise #ntil the slide $egins tocontact the grinding wheel.
. 5ote the n#m$er (on the control)
at which contact is made.
&0. hile still mo%ing the slide $ackand forth" ad%ance the control
wheel grad#ally a$o#t three ticks
from the contact %al#e. At thispoint" grind for a while witho#tad%ancing the wheel while mo%ing
the slide $ack and forth" to ens#re
complete and e%en grinding.
&&. T#rn off the %ac##m and press the
%ac##m release %al%e (the $lack
t#$e from the slide holder
connacts to itB it is pressed towardsyo#). hen the hissing stops"
remo%e yo#r slide from the holder.(Try not to drag it" or it may getscratched).
&2. ry it off and see if its all frosted
e%enly. +f not" repeat the a$o%e
steps #ntil it is. o# sho#ld notneed more than fo#r ticks or so.
&3. 6nce its all frosted" make a note
of the position at which yo#
stoppedB yo#ll need it later. This%al#e is the Cero-thickness
position" the position at which the
grinding wheel contacts the glassslide.
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tep Three, *ark yo#r rock
o# need to decide where yo# will c#t
yo#r rock. This matters" especially with
rocks that ha%e a fa$ric. o# generallywill want to c#t a thin section on a plane
perpendic#lar to any planar fa$ric" $#t for
partic#lar p#rposes yo# may want thinsections in other orientations. *ark a line
on the rock with the harpie.
4ig#re &. :ock priorto c#tting. 8encil for
scale. 5ote that this
rock was not marked
$efore c#tting" $#tnormally it wo#ld $e.
tep 4o#r, #t the sla$
Dsing the sla$ saw in the $ack of theroom" yo# will c#t a sla$ from yo#r rock
along the line yo# marked.
&. 4irst clamp the sample in theholder so that the line is parallel to
the saw $lade" sticking o#t of the
holder. o# do not make yo#r firstc#t along this lineE
2. 4ind crank handle and attach to
s/#are protr#sion on tray. indthe tray a$o#t && t#rns away fromthe saw $lade. There is some
hysteresis" or 9slop9" so dont
co#nt crank t#rns where the trayisnt mo%ing. :emo%e the crank
handle.
3. lose the co%er" making s#re the
sides and $ottom are t#cked insidethe lip.
!. *ake the c#t. 4irst t#rn the switch
on to get the $lade mo%ing" then
t#rn the kno$ #ntil the weight$egins to fall.
'. 6nce the c#t is done (yo# can hear
it)" t#rn the $lade off and stop the
4ig#re &?. la$ saw.
5ote location for crankin $ottom center.
4ig#re &@. la$ sawcontrols. T#rn kno$ to
mo%e rock
intoFthro#gh $lade" and
switch start $ladet#rning (only t#rn on
with co%er completely
closedE).
4ig#re &. :ock ready
for first c#t. 5ote thatit sticks o#t extra far to
allow for second c#twitho#t remo%ing fromclamp.
4ig#re 20. After first
c#t. 5ext" close kno$"
p#ll tray $ack fromsaw" then mo%e tray
towards $lade a$o#t &&t#rns of the crankhandle.
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weight mo%ing $y t#rning thekno$ away from yo#.
. 8#ll the tray $ack to the $eginning"
and #se the crank to wind the$lade $ack to yo#r line" && real
t#rns (where the tray is mo%ing).
?. :emo%e the crank handle" and
close the co%er.
@. *ake the next c#t as yo# did thefirst. These two c#ts sho#ld $e
parallel planes a$o#t @-&0 mm
apart. The sla$ sho#ld fall onto the
catch tray $ehind the $lade.
4ig#re 2&. :eady forsecond c#t.
4ig#re 22. After
second c#t, sla$complete (piece lying
on catch tray at left).
lean #p the sla$
&. 4irst wash the sla$" the lefto%er
rock" and the first c#t piece (if
theres eno#gh to sa%e) to remo%e
any oil and grit from the sla$ sawprocess.
2. 5ext (while the rocks are drying)
set the lefto%er rock and the first
c#t piece on a paper towel to dry"$#t mark the sample n#m$er on
the towel. +ts %ery easy to mix #p
specimens at this point" $eca#seyo# may ha%e needed to c#t
thro#gh the n#m$er pre%io#sly
marked on the rock. Also" the firstc#t piece likely has no n#m$er.
6nce these are dry" re-mark them
with the sample n#m$er. + #seli/#id paper and an india ink pen"
followed $y nail polish once its
dry.
4ig#re 23. ashing oil
and dirt off the rocks
after sla$ c#tting.
4ig#re 2!. rying
speicmens with sample
n#m$er written on thepaper towel .
tep 4i%e, #t the chip
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o# need to red#ce the siCe of the sla$ toslightly smaller than a thin section. 4or
this yo# will #se the trim saw against the
$ack wall of the room. o# need to
caref#lly decide from what part of the sla$yo# want to c#t the section.
&. o# will #se a special rock-c#tting
$lade which is made of metal withdiamonds em$edded in it.
ssentially" s#ch $lades are narrow
grinding tools. o# can e%ensafely p#t yo#r finger on it as it
mo%es (if it is l#$ricated with
water)" howe%er yo# sho#ld not
p#t yo#r fingernail on it.
2. o# sho#ld wear eye- and ear-
protection gear when #sing this
saw.
3. tart the water #sing the %al%ea$o%e and to the right of the saw"
and start the $lade #sing the switch
to the right.
!. o# ;#st p#t the sla$ on theplatform and mo%e it into the
$lade. o# can #se a glass slide to
get the siCe correct (the chipsho#ld $e slightly smaller than the
slide).
'. After c#tting the chip" the side
from which the thin section will $ec#t m#st $e polished to remo%e
marks from the saw $lade. 4or
$est res#lts yo# can grind on eachof the fo#r wheels" $#t a #sea$le
section will res#lt from ;#st
grinding on the seccond (2!0 grit)wheel.
. As a$o%e" clean the grinding
4ig#re 2'. These
$lades are safe to
to#ch as long as theyare l#$ricated" $#t
dont p#t yo#r
fingernail on it.
4ig#re 2. The
platform mo%es" soyo# ;#st p#sh the sla$
thro#gh the $lade.
4ig#re 2?. 4inal c#t for
the chip.
4ig#re 2@. >rindingthe chip will remo%e
any saw marks from
the c#tting.
4ig#re 2. ashing the
chip.
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wheel when yo# are done with it.
tep ix, >l#e the slide to the chip
5ext" yo# attach the frosted side of theslide to the side of the chip yo# ;#st
gro#nd down. o# need to ens#re a
constant thickness of epoxy across thesection" or when yo# grind the section
down" one end will $e thicker than the
other.
&.
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o These materials now m#st
$e well-mixed" $#t whilecreating as few $#$$les as
possi$le. +n order to
achie%e this" + drag thecoffee stirrer in a sin#o#s
pattern first in one
direction" then in the samepattern rotated 0 degrees.
!. 6nce the epoxy is well-mixed"
spread a few drops across the top
(polished side) of the warmedchip.
'. *any rocks are poro#s (e%en somethat yo# might not expect) and yo#
m#st let the epoxy penetrate f#lly"or the thin section will not s#r%i%e.
o" spread epoxy" then wait for it
to soak in (' min#tes) then spreadmore epoxy. :epeat #ntil no more
epoxy soaks into the chip.
. 8lace the slide" frosted side down
on the epoxy. +ts $est to p#t one
side down" then let the other sidefall to a%oid trapping $#$$les.
?. *o%e the slide aro#nd with yo#r
finger or a pencil eraser. This wills/#eeCe o#t extra epoxy to achie%e
a constant thickness" and if yo#
work at it" yo# can remo%e most$#$$les this way as well. hile
doing this" $e s#re that the sample
n#m$er gets coated with epoxy.
@. Get this sit to c#re. heck itperiodically for the first '-&0
min#tes to $e s#re the slide has not
slid off the chip.
. The epoxy will c#re in a$o#t 20-30 min#tes. o not take the next
4ig#re 3. 8lacing
slide on chip" frosted
side down.
4ig#re 3?. *o%ing
slide aro#nd to expel
$#$$les and extra
epoxy" and coat samplen#m$er.
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step $efore that.
tep e%en, #t off the chip from theslide
5ow yo# ha%e a rock chip epoxied to a
glass slide. o# will next c#t most of the
chip off" lea%ing a thin slice attached.
&. 8lace a $lank glass slide on thegrinder to $lock the %ac##m.
2. T#rn on the water to the c#t-off
saw.
3. 8lace the slide on the c#t-off saw(note direction of gro#nd corner)
and t#rn on %ac##m to hold it. 1e
s#re edges of slide are lodgedagainst pins in holder.
!. T#rn on saw motor.
'. Dse the handle to mo%e the chip
into the $lade. >o %ery slowly" or
yo# can $reak yo#r slide and ha%eto start o%er.
. 6nce the chip is c#t off the slide"
retrie%e the chip from the water
tray and set it aside (it will likelyneed to $e la$eled with the sample
n#m$er).
?. T#rn off the %ac##m" and saw
motor.
@. Dsing the $#tton (as with the
grinder - see a$o%e)" $reak the
%ac##m. 6nce the hissing stops"remo%e yo#r slide from the saw.
4ig#re 3@ . lide withchip mo#nted in c#t-
off saw.
4ig#re 3 . lowlyc#tting off the chip
from the slide.
4ig#re !0 . hip nearly
c#t from slide.
4ig#re !& . hip and
slide separated.
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. :inse yo#r slide to remo%e anyparticles.
tep ight, >rind yo#r slide to the correct
thickness
o# m#st now grind away m#ch of the
rock that remains on yo#r slide" $#t not allof it. This is the step in which most thin
sections go $ad. The key is, go slow"
especially near the end.
&. 8lace a $lank glass slide on thec#t-off saw to $lock the %ac##m.
2. T#rn on the water to the grinder.
3. T#rn the control towards yo#
(co#nter-clockwise) a f#ll rotationto Cero.
!. 1e s#re the slide holder and the
slide are clean and free of any grit
or particles.
'. 8lace the slide on the grinder(maintaining the same orientation
#sing the corner yo# notched).
. T#rn on the %ac##m and grinder
motor.
?. *o%ing the slide $ack and forth
with the handle" grad#ally ad%ance
the control #ntil the slide contacts
the grinding wheel.
@. hile mo%ing slide $ack and forth
across the grinding wheel with the
$lack handle" grad#ally ad%ancethe control #ntil yo# reach a point
a$o#t &' ticks $elow yo#r 9Cero
%al#e9 (see step 2).
4ig#re !2 . Dngro#nd
slide mo#nted ingrinder holder.
4ig#re !3 . *o%ing
slide across grinding
wheel while ad%ancingcontrol (with right
hand).
4ig#re !! . hecking
the slide thickness#sing the microscope.
4ig#re !' . H#artC in a
thin section" way toothick.
4ig#re ! . H#artC in a
thin section" still fairlythick.
4ig#re !? . H#artC in a
thin section" still a $itthick.
4ig#re !@ . H#artC in a
thin section" now too
thin. At this point"m#ch of the remaining
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. :emo%e the slide (t#rn off the%ac##m" $reak the %ac##m with
the $#tton" then remo%e the slide)
and see if yo# can identify any
minerals in the section.
o +f yo# can" then proceed
slowly #ntil those minerals
achie%e the correct
maxim#m interferencecolor (e.g." /#artC sho#ld
show a maxim#m
interference color of a palestraw yellow)
o +f yo# cannot" thenad%ance one tick at a time
#ntil yo# can identify a
mineral. +f yo# are within 'ticks of yo#r Cero %al#e"
and yo# still cant identify
anything" stop and ask
someone who knows morethan yo#.
o >o slow" especially when
yo# are close to the correctthicknessE +ts /#ite easy to
go from slightly too thickto slightly too thin (or
gro#nd completely away)"even without advancing
the position control at all!
Tro#$leshooting
o Warning, *ost sections
fail at this stage $eca#seyo# are grinding too fastE
:emem$er" any time thegrinder makes noise
against a slide" yo# are
remo%ing rock. o# oftendont ha%e to ad%ance the
section has $een
gro#nd away.
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wheel at all to ;#st grind asmall thickness away.
o +f yo#r section comes o#t
with the minerals allcracked, you were
grinding too fast.
o +f yo#r section comes o#t
with the edges thin and the
center thick, you weregrinding too fast.
o +f yo#r section comes o#t
thick on one side and thin
on the other" yo# eitherdidnt frost the slide well"
or there was an #ne%en
epoxy layer.
tep 5ine (%ersion &), Add a co%er slip
+f yo# do not expect to perform chemicalanalysis on yo#r minerals in this thin
section" yo# sho#ld add a co%er slip toprotect the section from damage" andincrease the clarity o$ser%ed in the
microscope. This process is a simple one,
&. *ake s#re the section is clean and
free of grit or dirt.
2. 8lace it on the hot plate.
3. *ix #p a small $atch of epoxy and
hardener.
!. 8lace a small drop of epoxy on the
section.
'. rop a co%er slip on the drop.
. *o%e it aro#nd to expel $#$$les
4ig#re ! . 8#tting adrop of epoxy on the
gro#nd slide.
4ig#re '0 . ontainerfor co%er slips.
4ig#re '& . ropping aco%er slip on the slide.
8#t one end down firstin order to pre%ent
$#$$les.
4ig#re '2 . *o%ingco%er slip to spread
epoxy and expel$#$$les.
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and f#lly coat the section.
?. Get it c#re.
@. After it has c#red" there may $eextra epoxy on the top" sides" or
$ottom. o# can remo%e this" very
carefully" with a raCor $lade.
tep 5ine (%ersion 2), 8olish for lectronmicropro$e F *- analysis
+f yo# plan to perform chemical analysis
on yo#r minerals" then yo# need to polish
the section m#ch $etter than the grinderpolishes it. This is $eca#se these analysis
tools re/#ire a flat" smooth s#rface at the
micrometer scale. o# perform thispolishing step #sing different tools in a
different room.
The key diffference for o#r p#rposes here
is that yo# sho#ld stop grinding when thesection is still a little $it thick" $eca#se
yo# will $e remo%ing material d#ring the
polishing process.
The polishing apparat#s is located on thegro#nd floor" at the other end of the
$#ilding (near the I:).
(4#ll instr#ctions for polishing may $eadded to this doc#ment in the f#t#re. 4or
now" ask a knowledgea$le #ser for help).
tep Ten, lean #p the place
o# m#st clean the la$ thoro#ghly when
yo# are done #sing it. o# may store
samples in progress in one or more traysclearly la$eled with yo#r name and the
date. These trays are placed in the lower4ig#re '3. rying off 4ig#re '!. 6iling the
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ca$inets in the thin section la$ room" or(for grad st#dents) in the ca$inets in the
center of the ad;acent room.
&. *ake s#re that the grading wheelsare clean and dry (see instr#ctions
a$o%e).
2. ompletely dry off the dark metal
section holders on $oth the c#t-offsaw and the grinder.
3. 4or each of those two tools" spread
some oil on a paper towel" and
coat the dark metal portion
thoro#ghly with oil" then place theoiled paper towel #nderneath the
section holder.
!. mpty o#t the water from the%ac##m $ottle (co%ered with tape).
'. 8lace any epoxy stirrers crosswise
on the epoxy holder so that when
the epoxy dries" $oth can $ere#sed.
. *ark yo#r name in the log sheet.
?. T#rn off the lights and close the
door when yo# lea%e.
the section holder. paper towel.
4ig#re ''. 6iling thesection holder.
4ig#re '. Tool dried"
oiled" and paper towelplaced for storage.
4ig#re '?. :emo%ingt#$ing from %ac##m
$ottle.
4ig#re '@. mptyingthe %ac##m water
$ottle.
4ig#re '. poxy
stirrer and tray storedfor c#ring and re#se.
4ig#re 0. 4illing o#tthe log sheet.