Optical Min5

8/18/2019 Optical Min5

1/19

Optical Mineralogy in a Nutshell

Use of the petrographic microscope in

three easy lessons

Part III

© Jane Selverstone, University of New Mexico, 2003


2/19

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


3/19

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


4/19

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!


5/19

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


6/19

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


7/19

Cleavage

( cleavagesintersectingat *+-pyro)ene

.-'(-

( cleavagesintersectingat .-/'(-%amphibole


8/19

Cleavage

random fractures,no cleavage%

olivine


9/19

0winning

Presence and style of twinning can be diagnostic

0wins are usually most obvious in #$ upper polari!er in"


10/19

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 '"


11/19

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


12/19

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


13/19

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


14/19

7abit or form

bloc8y

acicular

bladed

prismatic

anhedral/irregular

elongate

rounded

fibrous

tabular

euhedral


15/19

7abit or form

bloc8y

acicular

bladed

prismatic

anhedral/irregular

elongate

rounded

fibrous

tabular

euhedral


16/19

9eview – techni&ues for identifying un8nown minerals

2tart in PPL%: Color/pleochroism: 9elief: Cleavages

: 7abit

0hen go to #$%: ;irefringence

: 0winning: 5)tinction angle:


17/19

>o to $esse or similar boo8…

• Chemical formula• 2ymmetry•


18/19

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


19/19

6n to real roc8s…

…good luc8 and have funE

Optical Min5

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