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Variegated Purple

Submitted by Raven Mueller on Wed, 2014-07-09 08:34
Stone Type (Commercial): 
Availability: 
Available
Physical Data
Munsell Color(s): 
Geology
Stone Type (Lithologic): 
Grain Size: 
Fine
Very Fine
Petrographic Description: 

Specimen: 2014-014
This specimen is a red slate. The color of the specimen suggests the presence of significant hematite, limonite, and or siderite. 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 .15 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 are abundant and occupy about 30 to 40 percent of slide area with a maximum crystal dimension of about .08 mm, the vast majority are under .03 mm. Carbonate crystals are a mix of anhedral and rhombohedral forms. Opaque minerals including iron hydroxides make up approximately 15 to 25 percent of slide area. The vast majority of iron hydroxide minerals are under .01 mm. Relict sedimentary features are faintly visible on macro-inspection of the slide. Under the microscope these patterns are perceptible as frequency differences in light (quartz/feldspar) and dark (opaques/iron hydroxides) minerals and the translucency of the aphanitic component. In the hand sample there are color changes that likely correspond to differences in oxidation conditions and parent material of the original sedimentary contributions; these are not visible in this slide. 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

Images

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Specimen ID
2014-014 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
2014-014 Specimen shown in non-polarized light.download image Specimen shown in cross-polarized light.download image

Quarry

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