Olivine Optical Mineralogy Properties 111a5v

Dari web: http://www.nslc.ucla.edu/pet/mineral_html/Olivine.html

Olivine Next Mineral

xpl 10*

ppl 20*

xpl 20*

ppl 20*

xpl 20*

ppl 5*

1. xpl 3rd order birefringence x5

2. ppl ideal crystal shape x5

3. xpl maximum birefringence x5

4. xpl extinction x5

7. ppl olivine in pyroxence x5

8. xpl olivine in pyroxence x5 group olivine system orthorhombic formula (Fe,Mg)2SiO4 optic biaxial neg / pos Too-Vee 46 - 98¡ relief.1 high pos min. index 1.636 / 1.879 color colorless, yellow pleochroism yes birefringence.1 0.033 - 0.052 cleavage no elongation yes extinction parallel angle 0¡ alteration iddingsite, chlorophaeite habit.1 subequant, anhedral (aggregates), euhedral occurence igneous (granitic, volcanic, mafic, ultramafic) meta- morphic (skarn), sedimentary TwoV 1 2 relief 3 pleochroism.2 yellow, orange birefringence 9 12 13 cleavage.2 ( {010}, {110} not seen in thin section)

dari web: http://www.brocku.ca/earthsciences/people/gfinn/minerals/olivine.htm

OLIVINE General Formula: (Fe,Mg)2SiO4

System: Orthorhombic

Sample: PT-96

Euhedral to subhedral olivine Olivine phenocrysts, phenocrysts exhibiting nd rd irregular fractures, exhibiting 2 to 3 in a plagioclase order interference colours microlite matrix Field of View = 4.0 mm, Crossed Field of View = polars 4.0 mm, plane light

Block diagram showing the relationship between the crystallographic axes and the indicatrix axes.

Optical Properties Colour Pleochroism

usually colourless, darker colours correspond to higher iron content non pleochroic

Form

generally subequant anhedral grains or aggregates in intrusive and metamorphic rocks. Equidimensional or elongated euhedral grains in volcanics

Relief RI

high positive n = 1.636-1.827 n = 1.651-1.869 n = 1.669-1.879

Cleavage

not observed

Birefringence 0.033-0.052 Interference up to third order

Twinning

not common

Colours Interference Figure Optic Sign 2V

biaxial positive or negative 46-98°

Optic Orientation

elongate grains have parallel extinction and may be either length fast or slow

Composition

minor substitution of Alteration Mn, Zn, Ca, Ni, Cr or Al for Fe and Mg

Occurrence

pure Fo (Mg-rich) is Distinguishing high birefringence, restricted to Features distinctive fracturing, lack metamorphosed of cleavage, and alteration carbonates, intermediate products. Fe-Mg olivine is common in mafic and ultramafic igneous rocks, Fe-rich olivine occurs in felsic rocks.

commonly alters to iddingsite and chlorophaeite, which are really mixtures of various minerals which cannot be identified, and serpentine. Alteration progresses from the edge and along cracks

Dari web: http://www.science.smith.edu/geosciences/petrology/petrography/olivine/olivine.html

Smith College - Geology 222b - Petrology Petrographic Data File

Olivine Property

Value

Comments Complete solid solution between Mg2SiO4 (forsterite) and Fe2SiO4 (fayalite).

Formula

(MgFe)2SiO4

Crystal System

orthorhombic

Crystal Habit

granular masses or rounded grains

Cleavage

no distinct cleavage

conchoidal fracture

Color/Pleochroism

Olive or yellowish-green in hand samples. Colorless to pale green in thin section. Weak, pale green

Can be a yellowish color when rich in iron.

pleochroism in thin section.

Optic Sign

Biaxial (-); or Biaxial (+)

2V

82-90; forsterite 46-90; fayalite

if 2V =82-90 it is forsterite and Biaxial (+) if 2V=46-90 it is fayalite and Biaxial (-) Varies depending on composition. Click here for graph.

Optic Orientation

X=b Y=c Z=a

O.A.P. = (010) Refractive Indices alpha = beta = gamma = delta = Max Birefringence

1.635-1.827 1.651-1.869 1.670-1.879 0.035-0.052 0.033 - 0.052

Elongation Extinction

parallel

Elongate crystals display parallel extinction.

Dispersion

Distinguishing Features

Colorless to olive green in thin section. Second-order interference colors. High relief. Lack of cleavage. H= 7. G = 3.22 to 4.39. Specific gravity increases and hardness decreases with increasing Fe. Streak is colorless or white.

Occurrence

Occurs in a wide variety of volcanic rocks, both as phenocrysts and as groundmass. Olivine with intermediate Fe-Mg composition is common in mafic and ultramafic volcanic rocks and plutonic igneous rocks. Iron rich olivines occur in alkaline and acid plutonic rocks.

Editors

Micehelle Arsenault (01), Jamie Mitchell (03), Angelie Peterson (02), Cheryl Mawaka (04), Lauren Magliozzi (12)

Photomicrograph of olivine in plane light. Olivine typically displays pale green pleochroism and no distinct cleavage. Mag. 10x.

Photomicrograph of olivine under crossed polarized light. These crystals show 2nd order interference colors. This sample also shows some plagioclase feldspar with albite twinning.

Photomicrograph of olivine in basalt in crossed polars with cleavage planes parallel to crosshairs of microscope, showing "extinct" view. Select the image and then move cursor over image to view the stage rotated 45 degrees, where the mineral shows maximum transmitted light. These two images demonstrate the extinction angle of olivine. Photomicrograph of olivine in basalt (ED99-J) in plane light. Select image and then move cursor over image to view in crossed polarized light, where crystals show high bifringence. Magnification 1.5x.

Photomicrograph of olivine phenocrysts, in a matrix of Hawaiian basalt, in plane light. Select image and then move cursor over image to view in crossed polarized light, where crystals show high birefringence. Magnification 5x.