Smith College - Geology 222b - Petrology

Petrographic Data File



Commonly pure TiO2 ; Subsitution for Ti may include Fe, Ta, Sn, Nb ; possible presence of Cr and V

Crystal System Tetrahedral  
Crystal Habit Prisms, Contact Twins (elbow or cyclic-shaped){101} "needle-like" cyrstals in thin section
Birefringence 0.29

Extreme/distinct but often masked by rich mineral color ; intense birefringence makes determining sign of elongation impractical

Cleavage {110} and{010} Barely visible in thin section

Optic Sign

Uniaxial (+)

Hardness 6-6.5
Specific Gravity 4.23-5.5

Reddish-Brown; Yellow-Brown; interference figures can have numerous isochromes; weak pleochroism (Omega > Epsilon)

Refractive Index

Omega: 2.605-2.613
Epsilon: 2.899-2.901

Distinguishing Features Extreme positive relief in thin section; rich yellowish-reddish brown color in thin section
Occurrence Very stable in weathering envirnments, common in clastic sediments; Fine fibers found as inclusions in quartz; Large crystals found in Pegmatites; Placer deposits for Titanium
Editors Hillary Friedman ('08)


Photomicrograph of anahedral grains in plane polarized light. From a Blue Shist, Cyros, Greese. (JBB-99-15E)

Click on the thumbnail to see a larger ppl/xpl rollover image.

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