Unfading Gray

Submitted by Raven Mueller on Tue, 2014-07-08 10:01
Stone Type (Commercial): 
Physical Data
Munsell Color(s): 
Stone Type (Lithologic): 
Grain Size: 
Very Fine
Petrographic Description: 

Specimen: 2014-006

This specimen is a gray slate. The color of the specimen suggests significant graphite dust presence. Owning to the aphanitic nature of the material, many of the constituent minerals in this specimen cannot be identified through microscopy. Quartz/feldspar grains are common with a maximum dimension of .12 mm, most are smaller. Various species of mica presumably form the majority of the specimen’s fabric, but these are generally too small to be individually perceived. Identifiable crystals of mica are mostly .12 mm and less in length. Visible mica crystals show orientation preference. Carbonate minerals occupy approximately 3 percent of slide area with a maximum crystal dimension of about .10 mm. Most carbonate crystals have rhombohedral edges. Opaque minerals are also rare and make up less than 1 percent of slide area. Clearly relict sedimentary features are visible on macro-inspection of the slide in the form of faint banding. These are not easily visible under the microscope. Overall the lack of more significant grain elongation and orientation prevalence indicates very low grade metamorphism. This may be due to the slide’s orientation, which is perpendicular to the likely direction of maximum tectonic stress.

7/14/15 MP


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Specimen ID
2014-006 Image of specimen in dry conditions. Finish: Natural cleftdownload image Close-up image of specimen in dry conditions. Finish: Natural cleftdownload image

Thin Sections

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Specimen ID Non-polarized Cross-polarized
2014-006 Specimen shown in non-polarized image Specimen shown in cross-polarized image


NOTE: Quarry locations are approximate.

Calder Quarry
United States
Vermont US

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