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Optical Mineralogy in a Nutshell
Use of the petrographic microscope in
three easy lessons
Part III
© Jane Selverstone, University of New Mexico, 2003
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JENIS PENGAMATANJENIS PENGAMATAN
ORTOSKOPISORTOSKOPIS
KONOSKOPISKONOSKOPIS
Sinar-sinar yang datangnya sejajarSinar-sinar yang datangnya sejajar
Sinar-sinar yang datangnya kerucut (lensa kndensr!Sinar-sinar yang datangnya kerucut (lensa kndensr!
PP" (nikl sejajar!PP" (nikl sejajar!
#P" (nikl $ersilang!#P" (nikl $ersilang!
%arna& 'lekrise& )a$it ($entuk!& indek $ias&%arna& 'lekrise& )a$it ($entuk!& indek $ias&$ela)an& relie*& ukuran$ela)an& relie*& ukuran
+ias rangka' (+,!& rientasi& 'eadaan&+ias rangka' (+,!& rientasi& 'eadaan&
su$u 'tik& tanda 'tik& ke$aransu$u 'tik& tanda 'tik& ke$aran
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IENTI,IKASI MINERA"IENTI,IKASI MINERA"
OPA.OPA.
TEM+/S 0A1A2ATEM+/S 0A1A2A((Trans'aranTrans'aran!!
ISOTROPISOTROP
ANISOTROPANISOTROP
Tak terjadi 'eru$a)an 3arnaTak terjadi 'eru$a)an 3arna
Terjadi 'eru$a)an 3arnaTerjadi 'eru$a)an 3arna
Tak ada $ias rangka' (+,!Tak ada $ias rangka' (+,!
Terda'at $ias rangka' (+,!Terda'at $ias rangka' (+,!
0nt)4 Mineral $iji)& gelas0nt)4 Mineral $iji)& gelas
0nt)4 R,M0nt)4 R,M
Mikrsk' PlarisasiMikrsk' Plarisasi
Mengacu 'ada indek 3arnaMengacu 'ada indek 3arna
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MINERA" PEM+ENT/K +AT/ANMINERA" PEM+ENT/K +AT/AN
MA,IKMA,IK
,E"SIK,E"SIK
Relie* tinggiRelie* tinggi+er3arna+er3arna
+, kuat+, kuat
Relie* renda)Relie* renda)
Tak $er3arna5 trans'aranTak $er3arna5 trans'aran
+, lea)+, lea)
Mineral SilikatMineral Silikat
Mineral Nn-SilikatMineral Nn-Silikat
Oksida ()eatit& agnetit& rutil!Oksida ()eatit& agnetit& rutil!Sul*ida ('irit& s'alerit& galena& kalk'irit!Sul*ida ('irit& s'alerit& galena& kalk'irit!P)s'at (a'atit!P)s'at (a'atit!Sul*at (an)idrit& gi'su!Sul*at (an)idrit& gi'su!
Kar$nat (kalsit& aragnit& dlit!Kar$nat (kalsit& aragnit& dlit!
(Seri +3en& 6789!(Seri +3en& 6789!
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A few new properties, and then some review…
0lea:age – number and orientation of cleavageplanes
T3inning – type of twinning, orientation
E;tinctin angle – parallel or inclined? Angle?
1a$it – characteristic form of mineral
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Cleavage
Most easily observed in PPL upper polari!er out",but visible in #$ as well
• $o cleavages% &uart!, olivine• ' good cleavage% micas
• ( good cleavages% pyro)enes, amphiboles
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Cleavage
( cleavagesintersectingat *+-pyro)ene
.-'(-
( cleavagesintersectingat .-/'(-%amphibole
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Cleavage
random fractures,no cleavage%
olivine
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0winning
Presence and style of twinning can be diagnostic
0wins are usually most obvious in #$ upper polari!er in"
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0winning 1 some e)amples
Clinopyro)ene augite"
Plagioclase
• 2imple twin on 3'4
• 2imple Carlsbad" twin on '"
• Pericline twin on h'"
• Polysynthetic albite twins on '"
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5)tinction angle
5)tinction behavior is a function of the relationshipbetween indicatri) orientation and crystallographicorientation
nε
nωa=X
c=Z
b=Y
c
a
b
Z
X
Y
parallel e)tinction inclined e)tinction
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5)tinction angle – parallel e)tinction
• All unia)ial minerals show parallel e)tinction• 6rthorhombic minerals show parallel e)tinction
this is because )tl a)es and indicatri) a)es coincide"
PPL #$
orthopyro)ene
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5)tinction angle 1 inclined e)tinction
Monoclinic and triclinic minerals%indicatri) a)es do not coincide with crystallographic a)es
0hese minerals have inclined e)tinction and e)tinction angle helps to identify them"
clinopyro)ene
e)tinctionangle
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7abit or form
bloc8y
acicular
bladed
prismatic
anhedral/irregular
elongate
rounded
fibrous
tabular
euhedral
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7abit or form
bloc8y
acicular
bladed
prismatic
anhedral/irregular
elongate
rounded
fibrous
tabular
euhedral
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9eview – techni&ues for identifying un8nown minerals
2tart in PPL%: Color/pleochroism: 9elief: Cleavages
: 7abit
0hen go to #$%: ;irefringence
: 0winning: 5)tinction angle:
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>o to $esse or similar boo8…
• Chemical formula• 2ymmetry•
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Another e)ample
0hen read te)t re color , pleochroism , habit , cleavage , twinning ,distinguishing features , occurrence – ma8e sure properties matchyour observationsB @f not, chec8 another mineral…
Crystallographic a)es% a, b, c
@ndicatri) a)es% #, , D or ε, ω
6ptic a)es
Cleavages
5)tinction angles
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6n to real roc8s…
…good luc8 and have funE