Dakota Mahogany Sunset

Submitted by Raven Mueller on Tue, 2014-07-08 08:28
Stone Type (Commercial): 
Physical Data
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Stone Type (Lithologic): 
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Specimen: 2014-004

This sample is a plutonic rock dominated by mostly anhedral feldspar and a lesser amount of quartz. The crystalline structure is generally coarse. Maximum crystal dimension is 13.5 mm (feldspar) and minimum is .1 mm (quartz). Quartz grains are notably smaller on average than feldspar grains. Modal grain size is around 3 to 5 mm for feldspar and .5 to .75 mm for quartz. There are a variety of feldspar twinning patterns including tartan (microcline), Carlsbad, and albite. Grain boundaries range from smooth curving to substantially consertal sutured. The latter is particularly common among quartz and feldspar grain boundaries. Intergrowth textures include microperthitic involving multiple species of feldspar and granophyric with plagioclase intergrown with quartz. Accessory minerals include biotite, which is common at about 10 percent of slide area. A green-brown amphibole (birefringence .012, biaxial -) is present in low quantities at less than 5 percent. Opaques are also relatively rare and comprise less than 5 percent of slide area. Other noted minerals include a single zircon crystal and several instances of a highly birefringent mineral too small to identify. There are slight signs of insipient weathering of feldspars with many grains presenting a dusty look. What is likely sericite is present in small patches (~10 µm) on some feldspar grains. Rarely, grain boundaries and cracks in grains have begun to fill with reddish brown clay material (>20 µm in width).
7/8/2015 MP


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Specimen ID
2013-004 Image of specimen in dry conditions. Finish: Polisheddownload image

Thin Sections

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Specimen ID Non-polarized Cross-polarized
2013-004 Specimen shown in non-polarized image Specimen shown in cross-polarized image


NOTE: Quarry locations are approximate.

Sunset Quarry
48391 150th St.
57252 Milbank , South Dakota
United States
45° 12' 26.6004" N, 96° 31' 19.2" W
South Dakota US

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