Unfading Mottled Green and Purple

Submitted by Raven Mueller on Wed, 2014-07-09 08:25
Stone Type (Commercial): 
Physical Data
Munsell Color(s): 
Stone Type (Lithologic): 
Grain Size: 
Very Fine
Petrographic Description: 

Specimen: 2014-012

This specimen is a brown-green slate. The color of the specimen possibly suggests the presence of chlorite as well as hematite and or limonite. 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 .1 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 and show some orientation preference. Carbonate minerals occupy about 1 to 3 percent of slide area with a maximum crystal dimension of about .1 mm, the vast majority are under .02 mm. Carbonate crystals are a mix of anhedral and rhombohedral forms. Opaque minerals, including iron hydroxides make up approximately 5 to 10 percent of slide area. Relict sedimentary features are slightly visible on macro-inspection of the slide in the form of faint banding. These are difficult to discern under the microscope and hinted at only by slight changes in light (quartz/feldspar) and dark (opaques/iron hydroxides) mineral frequencies and the translucency of the aphanitic component. 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.
7/16/14 MP


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Specimen ID
2014-012 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
2014-012 Specimen shown in non-polarized image Specimen shown in cross-polarized image


NOTE: Quarry locations are approximate.

Big Bear Slate Quarry
100 Hilltop Rd.
Poultney , Vermont
United States
43° 27' 28.0692" N, 73° 14' 2.868" W
Vermont US

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