araucaria1959 Posted March 28, 2013 Share Posted March 28, 2013 Hello, there are (purported) pyritised trilobites from the Alnif area of Morocco on the market. They are in the same grey (limestone) matrix like the usual black ones. Pyritised fossils may occur in black shales and were formed under anoxic, hydrogen sulphide-rich conditions. An example for them are the pyritised trilobites from the Hunsrueck shales from Germany. So I wonder whether pyritised trilobites can occur in the same grey limestones which usually yield the dark-grey, black or brownish trilobites which show no signs of any pyritisation. I show here as an example Metacanthina from the Alnif area, but there are also some other species with this purported sort of preservation on the market. My question: are they real or are the fakes? If so, are they faked completely, or is only the "pyritisation" faked? There are some traces of "golden colour" on the matrix of the specimen I show here (e.g., close to the glabella). This makes me think about the possibility that (possibly true) "normal" trilobites were artificially covered by a stain that gives the impression of being pyritised, or treated with a soft brass brush? Thanks, araucaria1959 Link to comment Share on other sites More sharing options...
jpc Posted March 28, 2013 Share Posted March 28, 2013 I know that pyrite fossils in gray shales in New york state occur in the same layer as regular ole black ones. So, yes, pyrite and blackness can co-exist, from my experience. Link to comment Share on other sites More sharing options...
Shamalama Posted March 28, 2013 Share Posted March 28, 2013 It could be that the black ones just need a light brushing to get the golden pyrite look. Pyrite (FeS2) can oxidize to Limonite (FeO(OH)·nH2O) which is black in color. -Dave __________________________________________________ Geologists on the whole are inconsistent drivers. When a roadcut presents itself, they tend to lurch and weave. To them, the roadcut is a portal, a fragment of a regional story, a proscenium arch that leads their imaginations into the earth and through the surrounding terrain. - John McPheeIf I'm going to drive safely, I can't do geology. - John McPheeCheck out my Blog for more fossils I've found: http://viewsofthemahantango.blogspot.com/ Link to comment Share on other sites More sharing options...
piranha Posted March 28, 2013 Share Posted March 28, 2013 This paper mentions pyrite occurring in many phases of Hamar Laghdad and frequently associated with trilobites. Looks good to me! Peckmann, D.G.J., Walliser, O.H., Riegel, W., & Reitner, J. (1999) Signatures of hydrocarbon venting in a Middle Devonian carbonate mound (Hollard Mound) at the Hamar Laghdad (Antiatlas, Morocco). Facies 40(1):281-296 Link to comment Share on other sites More sharing options...
Foshunter Posted March 28, 2013 Share Posted March 28, 2013 You can use a brass brush on a black fossil and give it a golden look as brass is softer than steel, don't know if this the case-----Tom Grow Old Kicking And Screaming !!"Don't Tread On Me" Link to comment Share on other sites More sharing options...
araucaria1959 Posted March 28, 2013 Author Share Posted March 28, 2013 That's exactly what I was afraid of ... especially because of the golden traces on the matrix in front of the glabella ... On the other hand, a hydrocarbon venting seems to me a plausible explanation for pyritisation in a facies dominated by limestone. araucaria1959 Link to comment Share on other sites More sharing options...
PRK Posted March 28, 2013 Share Posted March 28, 2013 I have always had my doubts about "pyrite" fossils, as once I was experimenting on different tecniques to prepare crinoids, and one of the techniques I tried was a brass brush. It made the crinoid LOOK, "dead on solid pyrite". when in reality it wasnt at all, and although they were beautiful, when done properly, left the matrix uneffected. Link to comment Share on other sites More sharing options...
Foshunter Posted March 31, 2013 Share Posted March 31, 2013 Just for grins, I took a smooth black baculite, photo a little out of focus, and applied a brass brush to one half and instantly the Midas touch.----Tom Grow Old Kicking And Screaming !!"Don't Tread On Me" Link to comment Share on other sites More sharing options...
PRK Posted March 31, 2013 Share Posted March 31, 2013 Thanks FH- (chuckle) good one! Link to comment Share on other sites More sharing options...
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