Nikol Sejajar

5/26/2018 Nikol Sejajar

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IDENTIFIKASI SIFAT OPTIKMINERAL


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MIKROSKOP POLARISASI


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Tahap Identifikasi

ortoskop nikol sejajar: warna,

pleokroisme, belahan,pecahan, relief,

indeks bias, ukuran mineral

ortoskop nikol silang: warna

interferensi, Bf, orientasi optik, sudut

pemadaman, kembaran.

konoskop: sumbu optik, tanda optik,

sudut 2V


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NIKOL SEJAJAR

Warna

pleokroisme,

belahan, pecahan,

relief,

indeks bias


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Ortoskop Nikol Sejajar

Warna merupakan pencerminan dari

kenampakan daya serap atau absorpsi

panjang gelombang dari cahaya yang

masuk pada mineral anisotropic.

Idiochromaticadalah warna asli mineral

Allochromaticadalah warna akibat adanya

pigmen lain seperti inklusi kristal-kristal

halus atau adanya elektron-elektron dari

logam-logam transisi (Cr, Fe, Mn, dll).

1. Warna


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Idiokromatik

allokromatik


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Gejala perubahan warna mineral pada

ortoskop tanpa nikol atau nikol sejajar bila

meja objek diputar hingga 90, disebut

dengan pleokroisme.

2. Pleokroisme

Jenis-jenis pleokroisme mineral dapat dibagi kedalam 2

(dua) golongan, yaitu :

Dwikroik (dichroic), bila terjadi perubahan dua warna

yang berbeda, contoh pada mineral bersistem kristalhexagonal dan tetragonal.

Trikroik (trichroic), bila terjadi perubahan tiga warna yang

berbeda. Terjadi pada mineral dengan sistem kristal

ortorombik, monoklin dan triklin.


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Bentuk-bentuk mineral dapat dibagi kedalam

tiga bagian, yaitu :

Euhedral, bila kristal dibatasi oleh bidangkristalnya sendiri.

Subhedral, bila kristal dibatasi hanya sebagian

bidang kristalnya sendiri.

Anhedral, bila kristal sama sekali tidak dibatasi

oleh bidang-bidang kristalnya sendiri.

Bentuk Mineral


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Klorit anhedral

Olivin euhedral

Plagioklas subhedral

Kuarsa

hexagonal


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Belahan (Cleavage)

Setiap mineral mempunyai kemampuan dan

kecenderungan untuk terpisah menjadi bagian yang lebih

kecil. Apabila bidang-bidang tersebut berbentuk lurus

dengan arah tertentu sesuai dengan bentuk kristalnya,

bidang tersebut adalah belahan (cleavage).

Apabila bidang-bidang tersebut tidak dikontrol olehbentuk kristalnya (struktur atom), tetapi dikontrol

oleh faktor lain seperti kembaran, maka bidang

tersebut dinamakanparting.

Jika bidang-bidang kecil dari mineral tidak lurus

dengan arah yang tidak teratur dan tidak dikontrol

oleh struktur atomnya, maka bidang tersebut

adalah pecahan (fracture).


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Indeks bias

Indeks bias merupakan fungsi dari perjalanan

sinar di dalam medium yang berbeda.


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Relief suatu kenampakan yangtimbul akibat adanya

perbedaan indeks biasmineral dengan media

yang ada di sekitarnya.


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Indeks Bias


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Plagioclase and Augite in a Diabase

The photos show mostly labradorite (a variety of plagioclase) with several grains of augite(a variety of

clinopyroxene). The labradorite is clear and the augitehas a typical dusty geen-gray color in PP light. Theplagioclase exhibits well developed albite twins, giving a zebra-striped appearance in XP light. Plagioclase,

especially plagioclase in igneous rocks, has a tendency to alter to micas and clays over time. This sample is

fairly fresh, but some plagioclase grains are slightly altered -- the alteration is visible as a sort of fine grained

grunge on grains near the top center of the photo. Note that the augite has significantly higher reliefthan the

labradorite.
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cpx.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cpx.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cpx.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cpx.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cpx.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cpx.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htm


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Plagioclase, Hornblende, Quartz and Biotite in a Gneiss

The clear minerals (PP) in this thin section are plagioclase (twinned) and quartz(not twinned). The green mineral (PP) is

hornblendeand the brown mineral is biotite(PP). The biotite is pleochroic, and some grains have a color similar to that

of the hornblende. The two can be tough to distinguish, but biotite has a more flakey (micaceous) habit.

Note the complex twinningin the plagioclase; there are two sets of twinsnearly perpendicular in the largest grain. In

other grains the twinningis discontinuous.
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/biotite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/pleoch.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/pleoch.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/biotite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htm


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Microcline with Quartz, Hornblende and Biotite

These photos show several grains of microcline (K-feldspar) with well developed cross-hatched twinning(XP).Quartzand plagioclaseare also present; they have color and interference colorssimilar to microcline's but lack

microcline twinning. Brown biotiteand green hornblendecan be seen in the PP view. One hornblendegrain

has a diamond shape and shows hornblende's characteristic two cleavagesat angles of 60oand 120o. A few

grains of magnetite are in the lower right.
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/biotite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cleavage.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cleavage.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/biotite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htm


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Epidote in a Highly Altered Basalt

The photos show epidote that has filled an amygdule in a highly altered basalt. The colorof the epidote is

typical: a sort of off-color yellow-green. The interference colors, too, are classic: various shades of pastels

within individual grains. The opaque material around the amygdule is a mixture of glass, hematite and chlorite.

Note several bubblesintroduced when the thin section was made.
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/pleoch.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/bubbles.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/bubbles.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/pleoch.htm


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Epidote and Hornblende in a Mafic Schist

The photos show pleochroichornblende(green hues; PP) and epidote (clear; PP) in a mafic schist. Note the

epidote grains show multiple interference colorscreating zones or concentric rings in most grains (XP). Alsonote that some of the hornblendeshows a hint of a diamond shape and of amphibole's characteristic 60o-120o

cleavage angle.
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/pleoch.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cleavage.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/cleavage.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/pleoch.htm


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Chlorite, Glaucophane and Epidote in a Blueschist

Green chlorite, blue glaucophane(an amphibole), clear white micaflakes (bottom center and right) and a

number of small high-reliefepidote grains (most are wedge-shaped) are visible in PP light. In XP light thechloriteshows anomalous interference colors, the glaucophane shows 2nd order interference colors, in places

somewhat masked by the blue colorof the mineral. The mica flakes show obvious mottled 2nd order

interference colors.The epidote grains are hard to pick out in XP light
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/naamph.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/muscovite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/pleoch.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/pleoch.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/muscovite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/naamph.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htm


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Titanite (sphene) in a Quartz Monzonite

This view shows a titanite "wedge" surrounded by magnetite, quartzand feldspar, and minor epidoteand chlorite. The

titanite has very high reliefand its interference colorsare of such high order that they are hard to identify. The "wedge"

or diamond shape of this grain is typical for titanite when it is euhedral (in many rocks it is not). Just above and to the

right of the titanite is a compound grain composed of epidote(high order blue-orange-red interference colors) and

chlorite(green in PP, nearly extinct in XP). Also present are three grains of magnetite (opaque
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/epidote.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/epidote.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/epidote.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/epidote.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htm


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These photos show a large euhedral garnet in a sea of mostly omphacite(a high pressure sodic pyroxene),

titanite, and a few flakes of white mica. The garnetis slightly altered to chloritealong its edges; note the

anomalous interference colorsin the XP view. The omphaciteis pale green (PP) with interference colorsthat

range up to first order red (XP). In a few places, where higher-order colorscan be seen, the omphaciteis being

replaced by hornblende. The titanite crystals are small, have very high relief(PP), and appear as irregular

elongate grains, some of which have acute terminations. Several flakes of white micaare present -- they are the

clearest grains visible in the PP view.

Garnet and Titan ite in an Eclogite
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/garnet.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/muscovite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/garnet.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/muscovite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/muscovite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/garnet.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/muscovite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/napyrox.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/garnet.htm


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RutileThe views above show several large grains of brownish rutile (PP). The rutile is surrounded by mostly quartz(on

the left and bottom of the photo) and several flakes of clear micaon the right. Rutile has very highbirefringence. Just a hint of high order pastel interference colorscan be seen here (XP).

Although not distinctive in these photos, kyaniteis present just above the two large rutile grains, and also to

the left of the smaller grain near the center of the field of view. The kyanite has slightly higher reliefthan

surrounding minerals, but otherwise is hard to pick out. It is clear (PP) and shows first order gray interference

colors(XP).
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/muscovite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/kyanite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/kyanite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/muscovite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htm


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The PP view shows biotitein various shades of brown, clear quartz, and light yellow brown twinnedrutile.The

rutile is rimmed by an opaque mineral, probably magnetite. Minor sillimaniteis present as one high-reliefmassnear the right side, just below center. One grain of clear plagioclaseis just above the largest rutile. In the XP

view, the large black grain is quartzthat happens to be near extinction. Biotiteshows typical second order

interference colors. The rutile shows no distinct interference colorsbecause the color of the grain masks the

interference colors.

B iot i te-Si ll iman ite Sch ist
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/biotite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/sillimanite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/biotite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/biotite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/relief.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/sillimanite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/twinning.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/biotite.htm


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Epidote-Clinozoisite

The diamond-shaped original crystal was hornblendebut it has been replaced byother minerals. In PP light, chloriteand epidote both appear light green (but thechloritehas a more "micaceous" character). Under crossed polars (XP) they aredistinguished because the chlorite shows anomalous green-gray interference colorswhile the epidote shows upper second order interference colors. Th opaque mineral is

magnetite; quartzand feldsparsurround the amphibole grain.
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htm


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Jawab pertanyaan1. Tuliskan tujuan mempelajari Mineral Optik dan hubungannya dengan

mata kuliah yang telah saudara pelajari.

2. Mengapa dalam menganalisis sifat optik menggunakan mikroskopkhusus yaitu mikroskop polarisasi?

3. Jelaskan hubungan bagian-bagian mikroskop dengan sifat optik yangakan ditentukan.

4. Jelaskan cara penentuan batuan atau mineral yang akan dianalisis sifatoptiknya.

5. Jelaskan sifat cahaya jika mengenai medium kristalin, lengkapi dengangambar.

6. Jelaskan terjadinya addisi dan substraksi cahaya pada medium kristalin

7. Jelaskan perbedaan medium isotrop & anisotrop, disertai dengan contohmineral

8. Gambar dan jelaskan pembiasan cahaya jika melewati medium isotrop &anisotrop.

9. Jelaskan perbedaan sumbu-sumbu optik pada mineral uniaxial danbiaxial.

Kumpul besok, selasa 13 Maret 2012 jam 10.00 di Lab. Petrografi.


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Nikol Silang


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Nikol Silang

Identifikasi mineral secara optik dengan

ortoskop nikol silang, menggunakan

lensa polarisator dan analisator. Dengan

ketentuan bahwa arah getar polarisator

harus tegak lurus terhadap arah getar

analisator.


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Sifat-sifat optik yang diamati

adalah :

Warna interferensi,

Birefringence(bias rangkap),Orientasi optik,

Sudut pemadaman dan jenis

pemadamanKembaran


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Warna Interferensi

Warna interferensi adalah warna yangdihasilkan dari cahaya yang diteruskan melaluianalisator kepada mata pengamat. Warna

interferensi terjadi pada mineral anisotropkarena adanya selisih harga indeks bias sinarordiner dan sinar ekstraordiner. Rangkaianwarna interferensi terbagi menjadi beberapa

orde, mulai dari orde pertama hingga ordekeempat.


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Bias Rangkap (Birefringence)

Cahaya yang masuk dalam media anisotrop

akan dibiaskan menjadi 2 (dua) sinar, yang

bergetar dalam 2 (dua) bidang yang saling

tegak lurus. Harga bias rangkap merupakanselisih maksimum kedua indeks bias sinar yang

bergetar dalam suatu mineral.


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Epidote-Clinozoisite

The diamond-shaped original crystal was hornblendebut it has been replaced byother minerals. In PP light, chloriteand epidote both appear light green (but thechloritehas a more "micaceous" character). Under crossed polars (XP) they aredistinguished because the chlorite shows anomalous green-gray interference colorswhile the epidote shows upper second order interference colors. Th opaque mineral is

magnetite; quartzand feldsparsurround the amphibole grain.
http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/plagioclase.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/quartz.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/birefringence.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htmhttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/hornblende.htm


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Pada mineral yang mempunyai

sistem kristal tetragonal, hexagonal

dan trigonal, selisih indeks bias

maksimum terdapat pada sayatan

yang sejajar sumbuc kristalografi,

karena pada sayatan ini sinar yang

bergetar adalah sinar biasa

(ordiner) dan sinar luarbiasa

(extraordiner) yang sesungguhnya.


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Perjalanan Sinar pada Ortoskop

Nikol Silang yang Menghasilkan

Birefringence.

Pada medium anisotrop, cahaya

dari lampu akan terpolarisasi danketika masuk pada media

kristalin, cahaya tersebut

diuraikan menjadi 2 (dua)

cahaya yang saling tegak lurus.

Bidang getar kedua sinartersebut adalah OA dan OB

pada bidang elips yang tegak

lurus terhadap arah sinar.

Kedua sinar tersebut masuk ke

dalam analisator dandikumpulkan menjadi menjadi

satu getaran dalam bidang CD.

Kedua getaran tersebut akan

mengalami interferensi (Fresnel

& Arago).


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Orientasi optik

hubungan antara sumbu panjang kristalografimineral dengan sumbu indikatriknya (arahgetaran sinar). Pada umumnya sumbu

terpanjang kristalografi adalah sumbu-ckristalografi.

Tetapi pada kelompok filosilikat, umumnyasumbu-c kristalografi merupakan sumbu

terpendek, sedangkan yang terpanjang adalahsumbu-a kristalografi.


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Orientasi Optik a)

sumbu-c sejajardengan polarisator,

b) putar meja optic

45, c) Jika sumbu-

c sejajar dengansumbu indikatrik

sinar Z maka

orientasi optiknya

length-slow

(Nesse, 1986).


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Sudut Gelapan dan jenis Gelapan

(Extinction)

Gelapan atau pemadaman adalah keadaan

mineral pada kedudukan warna interferensi

minimum, terjadi apabila sumbu indikatriks

(arah getar sinar) mineral sejajar dengan arahgetar analisator atau polarisator.


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Jenis Gelapan

Gelapan sejajar (paralel), terjadi bila pemadamanberada pada posisi dimana sumbu panjangataupun belahan mineralnya sejajar sumbu-c dansejajar pula dengan benang silang (c ^ X,Z = 0atau c ^ X,Z = 90. Gelapan ini umumnya terjadipada sistem kristal tetragonal, heksagonal,trigonal,dan ortorombik.

Gelapan simetris, terjadi bila pemadaman padaposisi simetris (c ^ X, Z = 45). Umumnya pada

sayatan mineral system orthorombik, monoklin,misalnya pada jenis mineral piroksin danamphibol.


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Jenis Gelapan

Gelapan miring, gelapan jenis ini merupakanpemadaman yang terjadi pada posisi dimana

sumbu panjang kristal (belahan yang sejajar

sumbu-c) membentuk sudut dengan arah getar

analisator dan polarisator (c ^ X,Z = 1 - 44).

Gelapan bergelombang, gelapan jenis ini terjadi

karena keseluruhan mineral telah mengalami

tekanan namun belum sampai rekristalisasi

secara sempurna, umumnya pada pada kuarsa.


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Jenis-Jenis

Pemadamana) Paralel,

b) Miring

c) Simetri

d) Tidak

Mempunyai

Pemadaman

(Nesse, 1986)


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Kembaran

kembaran nampak sebagai lembar-lembar yang

memperlihatkan warna interferensi dan

pemadaman yang berbeda.

terjadi gangguan pada waktu proses kristalisasiyang menyebabkan kembaran tumbuh. Dapat juga

terjadi karena adanya proses deformasi pada waktu

kristal tersebut sudah terbentuk (kembaran

deformasi).


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Kembaran

Pada kembaran tumbuh, lembar-lembar

kembarannya tertentu dan bidang batasnya

lurus.

kembaran deformasi, lebar lembar

kembarannya berubah dan batasnya sering

melengkung.


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tugas

Diskripsi sifat optik :

Mineral Tektosilikat (Q, K-Feld, Feldspatoid)

Fotomikroskopis nikol sejajar & silang

Documents

Nikol Sejajar