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 Tetragonal  
Crystal Habit Prisms, contact twins (elbow or cyclic-shaped){101} "needle-like" crystals in thin section
Birefringence 0.286-0.296

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

Cleavage {110}good, {100} moderate: parting on {092} and {011} 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

Refractive Index

Omega: 2.605-2.613
Epsilon: 2.899-2.901

Distinguishing Features

Thin section characterized by very high relief and extreme birefringence; rich yellowish-reddish brown color with depth of color relating to ferric iron, niobium, and tantalum content


Fairly widespread accessory mineral in metamorphic rocks and as larger crystals in pegmatites; fine rutile needle inclusions fairly common in transparent quartz, intergrowths found with ilmenite

Editors Hillary Friedman ('08), Emily DeWitt ('19)


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

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

Viewed in plane polarized light, the rutile in this thin section mostly lack an acicular or prismatic shape, preferring a more angular, granular morphology. Notice the titanite rims on the rutile (ALP-23B)

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

WWW Images

Union College [under amphiboles]
Oxford University [image 127]

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