Question I am finding many concretions in shale and am wondering how so many different forms and colors can come from the same matrix. They are silver,gold, blue and combinations of all three colors. Is there any value in them?
Answer Concretions can be variable. The colors come from the various minerals that become mobile and are deposited. Gold can be sulfur compounds. Blue can be caused by copper, Red iron oxide. Copper can cause green color, blue, titanium. There is no set in stone rules because what causes apparent color is a an optic effect controlled at the atomic level in the mineral structure.
Their value is purely as curios to collectors or people who think they are pretty.
Here is a paper on what causes various metals to effect colors in minerals.
I can answer questions concerning physical and historical geology, environmental geology/hydrology, environmental consulting, remote sensing/aerial photo interpretation, G&G computer applications, petroleum exploration, drilling, geochemistry, geochemical and microbiological prospecting, 3D reservoir modeling, computer mapping and drilling.I am not a geophysicist.
I have 24 years experience split between the petroleum and environmental industries. I have served as an expert witness in remote sensing, developmental geologist, exploration geologist, enviromental project manager, and subject matter expert in geology and geophysical software development.
Organizations American Association of Petroleum Geologists
American Association of Photogrammetrists and Remote Sensing
Education/Credentials Bachelor and Master of Science
Registered Geologist in State of Texas