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Siltstone, Chalcedony (Var: Agate) : SiO2

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Copyright © Larry Maltby
 
 
minID: Q2Q-EXV

Siltstone, Chalcedony (Var: Agate) : SiO2

Copyright © Larry Maltby  - This image is copyrighted. Unauthorized reproduction prohibited.
Dimensions: 9.5 cm x 12.5 cm x 13.0 cm

This nodule shows an unusual deposition of material. The nodule is about the size of a large grape fruit. The dimensions given represent the size of the entire nodule but the photo is a cut face that shows the content of a large vesicle in the host basalt. In the upper right area is an agate with a badly fractured orange center and a gray border of chalcedony. The fractures in the agate are all filled with brightly colored iron oxides. This is very typical of the agates found in the Lake Shore Traps. The chances of finding gem material here is very small.

Of interest is the fact that the remainder of the vesicle contents is likely a fine grained siltstone. The nodule was found associated with what appears to be a clastic dyke with a system of veinlets that distributed sediments including silt, mud and sand into the adjacent empty vesicles in the host basalt.

The best way to see this is to enlarge the bottom portion of the specimen and note the texture and flow lines. There is even some indication of stratification. The porosity is likely the result of liquefaction that aided the transportation of the materials through the vein system. Some of the porosity was later filled with the deposition of quartz.


This photo has been shown 173 times
Photo added:15th Jun 2017
Dimensions:3000x4000px (12.00 megapixels)
Date/Time of Photo:12th Jun 2017 22:37:44
Camera:CANON PowerShot S100
Software:Adobe Photoshop Elements 12.0 Windows
Exposure time:1/1250s
Aperture:f/4.0
Focal Length:5mm
ISO speed:160
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