A Geoscience Digital Image Library

TitleCorderite hornfels, near Helena, Montana
DescriptionThis is a fine grained rock, so individual minerals are difficult to see. Dark grains of altered cordierite (up to 0.5 cm across) are in a sea of biotite, quartz and muscovite. The specimen is 8 cm across.
ChronostratigraphyPrecambrian Belt Sediment metamorphosed during the early Laramide (Late Cretaceous)
LithostratigraphyBelt Series
LocationUSA ▹ Montana. Near Helena.
PhotographerNessa Eull. 2001-04-10.
CollectionWard’s Collection of Classic North American Rocks #71.
Key wordshornfels, Montana, cordierite
Tech details882 KB. Hand specimen. Fujifilm FinePix S1Pro digital camera; 60mm AF Nikon micro lens.
GeoDIL number322