A Geoscience Digital Image Library

TitleThin section of biotite-hornblende granite
DescriptionThis is the cross-polarized view of biotite-hornblende granite in thin section. The gray areas are the plagioclase where you can see areas of alteration, for example in the extreme lower left hand corner of the photo. Biotite is the brown area with the black spots of magnetite. The colorful areas of pinks, greens, blues and yellow show the high interference colors of K-feldspar (microcline). The dark green is the hornblende. The gray area in the upper left corner and the white area is quartz, which when turned under the microscope, will show undulatory extinction.
ChronostratigraphyPost Archean (Probably Keweenawan)
Geologic provinceMinnesota River Valley Precambrian
LocationUSA ▹ Minnesota ▹ Stearns. Near St. Cloud.
PhotographerDarla Sondrol. 2001-08-29.
CollectionWard’s Collection of Classic North American Rocks #3.
Key wordsgranite, Minnesota, St. Cloud
Tech details553 KB. Thin section. Nikon FDX-35.
GeoDIL number1514