SEM-CL image of granite from Llano, Texas

This photo is a CL image from granite (Town Mountain Granite, Llano, Texas -- ~1.12 to 1.07 billion years old) and shows two minerals intergrown with each other. The bluish cross-hatched area is occupied by a grain of potassium feldspar (microcline), and the purple red-rimmed mineral in the upper half of the image is a grain of sodium feldspar (albite). Both mineral grains grew as the granite slowly melted, cooled and crystallized. The black areas were altered by low temperature fluids that circulated through the granite after it had solidified, and may also be late filled fractures and cavities (fluid inclusions). The reddish areas probably were altered and invaded by sodium feldspar at a later time, when younger granites intruded the already solidified Town Mountain Granite and led to circulation of hot water (hydrothermal fluids) along fractures and grain boundaries.

The photo was taken with an electron microscope where an electron beam scans over the surface of the sample and, one spot at a time, excites (CL) that is recorded by a special color-sensitive detector (GATAN Chroma-CL).
Originally uploaded in Integrating Research and Education:Geochemical Instrumentation and Analysis.

Image 10530 is a 500 by 500 pixel JPEG
Uploaded: Aug31 07

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Credit: Image by Juergen Schieber, Department of Geological Sciences, Indiana University. Instrumentation: SEM FEI Quanta-FEG 400 with Gatan Chroma CL.

Image Courtesy: National Science Foundation website
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