Semi-Weathering Gray

Submitted by Raven Mueller on Tue, 2014-07-08 10:05
Stone Type (Commercial): 
Physical Data
Munsell Color(s): 
Stone Type (Lithologic): 
Grain Size: 
Very Fine
Petrographic Description: 

Specimen: 2014-007

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 rare with a maximum dimension of .08 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.1 mm and less in length. Visible mica crystals show some orientation preference. Carbonate minerals occupy approximately 20 percent of slide area with a maximum crystal dimension of about .10 mm. These carbonate crystals have rhombohedral edges. Opaque minerals are also rare and make up less than 1 percent of slide area. There is also a vein of carbonate with a max width of 1.3 mm. The vein extends beyond the slide edges. It is composed of anhedral carbonate crystals with a maximum dimension of 1.1 mm. Twining is common in these carbonate grains along cleavage planes. Clearly relict sedimentary features are visible on macro-inspection of the slide in the form of banding. These are visible under the microscope by the increased presence of opaque minerals as well as a decrease in the translucency of the aphanitic cpmponent. 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
2014-007 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
2014-007 Specimen shown in non-polarized image Specimen shown in cross-polarized image


No quarry information available for this stone.

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