Petrography Microscopes

Contact information:

We welcome inquiries from faculty, students, and professionals. For further information contact
Dr. Ed Ripley

Email: | Phone: 812-855-1196


Petrography Microscopes: The department has a set of rooms dedicated to optical microscopy and photo-imaging. Research-grade polarizing microscopes allow examination of whole thin sections at the scale of 1 to 1, scaled to magnifications ⟩40X. Computer controlled digital cameras allow high-resolution images with scale bars to be created and used in research. Reflected light microscopy is also available. These instruments are kept in a separate room adjacent to our optical microscopy classroom, used for teaching intermediate and advanced classes in mineralogy, and in sedimentary, igneous, metamorphic, and ore petrology. Other digital cameras are available for photographing whole rock specimens for paleontology, and petrology.


Image description: A set of images of the same K-feldspar (Kfs) grain shows an example of the powerful application of cathodoluminescence (CL) imaging. (A) A back-scattered electron image shows that the Kfs grain is homogenous and clear, with minor albite patches (P) and arrays of micropores (MP). (B) The CL imaging reveals at least four generations of Kfs and healed fractures (yellow arrows). The angular fragments of luminescent Kfs (a) in the breccia are cemented with a weakly luminescent Kfs (b), then re-broken and cemented with a darker luminescent Kfs (c) and finally by a non-luminescent Kfs (d). These multiple generations of healed fractures produce a mosaic of domains with variable luminescence in the Kfs crystal. The CL image also shows fine scale twin planes and that the albite patches (P) are non-luminescent. (C) A plane polarized light image shows domains of clear and turbid (Tu) Kfs. The albite patches and surrounding Kfs are turbid as well. (D) A crossed polarized light image showing well-developed crosshatched twinning (T) that is discontinuous across grain boundaries (red arrows), with coarser twin planes compared with those observed in the CL image. The variably luminescent domains in (C) do not appear to correlate with the grain boundaries observed here. This set of images shows how CL imaging reveals hidden structures that are invisible with routine optical and BSE imaging. The healed fractures are secondary structures and thus, the variable fillings of Kfs that crosscut the brightly luminescent magmatic Kfs grain are interpreted as younger populations of Kfs that precipitated from an aqueous medium. The Kfs is from the Mattamiscontis Mountain granitic pluton in central Maine.