Gem News International Gems & Gemology, Winter 2023, Vol. 59, No. 4

Pyritized Triceratops Fossils from South Dakota


Figure 1. Triceratops fossils recovered from the Hell Creek Formation in South Dakota. Photo by SD Gem & Fossil.
Figure 1. Triceratops fossils recovered from the Hell Creek Formation in South Dakota. Photo by SD Gem & Fossil.

In recent years, the Hell Creek Formation spanning the Dakotas, Montana, and Wyoming has been extensively studied by paleontologists. This rock formation is home to fossils of various vertebrates, including dinosaurs such as Tyrannosaurus rex and triceratops. The author, an amateur paleontologist, recently unearthed a new dinosaur fossil site on privately owned land in Perkins County, on the northern edge of South Dakota.

Figure 2. The cut and polished piece of pyritized triceratops fossil on the left weighs 50.5 ct and measures 41.28 × 22.23 mm. The piece on the right weighs 22.5 ct and measures 31.75 × 15.88 mm. Photos by SD Gem & Fossil.
Figure 2. The cut and polished piece of pyritized triceratops fossil on the left weighs 50.5 ct and measures 41.28 × 22.23 mm. The piece on the right weighs 22.5 ct and measures 31.75 × 15.88 mm. Photos by SD Gem & Fossil.

Although multiple creatures are being uncovered at the site, closer examination of these fossils recovered revealed that they were from triceratops (figure 1). In addition, the fossils contained pyrite, an iron sulfide also known as “fool’s gold” that forms in sedimentary rocks, giving the fossils a striking metallic appearance. This discovery of pyrite inspired the author to cut and polish the fossils into pieces for collectors to display (figure 2). Sixteen pieces have been cut so far.

Only water was used for cutting, to avoid dust inhalation and to keep the specimens from turning black. A cerium oxide polishing compound was used for the finish, followed by a drying process. The pieces were then treated with an epoxy adhesive to prevent pyrite decay.

The newfound dinosaur site in the Hell Creek Formation of South Dakota holds the promise of unveiling more treasures from the past. As the author’s team and others dive deeper into the site, they hope to uncover additional fossils, providing insight into the long-lost world of dinosaurs.

Deven Fisher is an amateur paleontologist in Rapid City, South Dakota.