Phys.org has an article about “golden” fossils.  Germany’s Posidonia shale, which dates to the early Jurassic, was thought to contain pyritized fossils of sea life.  New research by a team at the University of Texas at Austin have found that the golden shine actually comes from phosphate minerals with yellow calcite.  Additionally, the chemical composition hints at how the fossils were formed.   The research was published in the journal Earth Science Reviews.

The fossils of the Posidonia Shale date back to 183 million years ago, and include rare soft-bodied specimens such as ichthyosaur embryos, squids with ink-sacs, and lobsters. To learn more about the fossilization conditions that led to such exquisite preservation, the researchers put dozens of samples under scanning electron microscopes to study their chemical composition.

“I couldn’t wait to get them in my microscope and help tell their preservational story,” said co-author Jim Schiffbauer, an associate professor at the University of Missouri Department of Geological Sciences, who handled some of the larger samples.

The researchers found that in every instance, the fossils were primarily made up of phosphate minerals even though the surrounding black shale rock was dotted with microscopic clusters of pyrite crystals, called framboids.

Thanks for the recommendation, George Witaszek!