The study of natural glass formations provides important clues about Earth’s violent past, particularly concerning extraterrestrial impacts. These objects, known as tektites, are terrestrial rock material melted and ejected during a high-velocity collision. This material cools and solidifies while traveling through the atmosphere. Bediasites are a significant and well-studied variety of these natural impact glasses, offering scientists a tangible record of a massive event that occurred millions of years ago.
Defining Bediasites and Tektite Classification
Bediasites are classified as splash-form tektites belonging to the North American Strewn Field, one of only four major tektite distribution areas globally. Tektites are grouped based on their chemical composition, age, and the geographic region where they are scattered, which is called a strewn field. Bediasites are chemically distinguished by their highly siliceous composition, meaning they contain a high percentage of silica glass.
This high silica content helps define their unique chemical signature, separating them from other tektite groups. Specific scientific analyses show that Bediasites possess a distinct enrichment in heavy noble gases like Xenon, with certain isotopic ratios far exceeding those found in other tektite groups. These chemical markers provide evidence that Bediasites were formed from a unique melt of terrestrial source material, primarily sedimentary rock, at the impact site. The North American Strewn Field also includes Georgiaites, which are chemically related but geographically distinct tektites found in the eastern United States.
The Origin Story: Impact and Formation
The formation of Bediasites began approximately 35.5 million years ago during the late Eocene epoch with a massive extraterrestrial impact event. A bolide, likely a comet or asteroid estimated to be about two miles in diameter, struck the shallow continental shelf. This collision occurred in what is now the lower Chesapeake Bay region of Virginia, creating the deeply buried Chesapeake Bay impact structure.
The extreme energy of the impact instantly vaporized the projectile and melted billions of tons of terrestrial target rock and sediment. This molten material was ejected at high speed, soaring out of the atmosphere on a ballistic trajectory. As the fiery droplets traveled across the continent, they rapidly cooled and solidified into glass while experiencing atmospheric friction upon re-entry. This process produced the characteristic glassy, often aerodynamically shaped, specimens. Radiometric dating of the glass confirms a weighted mean age of 35.3 million years for the Bediasites, precisely linking them to the Chesapeake Bay impact event.
Physical Characteristics and Geographic Distribution
Bediasites are typically dark brown to black in color, though some rare specimens show a slightly lighter, brownish-green hue. Their appearance is that of a natural glass, exhibiting a smooth, glassy texture when fractured and often containing internal flow lines and small, trapped bubbles. While the glassy material initially formed classic “splash forms” like spheres, teardrops, and dumbbells, most recovered Bediasites are worn.
The majority of recovered specimens are smooth, abraded pebbles because they have been subjected to millions of years of erosion and weathering since their fall. The geographic distribution of Bediasites is limited to the western portion of the North American Strewn Field. They are predominantly found in a narrow, approximately 140-mile-long strip covering about nine counties in the east-central part of Texas. This specific concentration is attributed to the geological layering of the late Eocene sediments where the tektites initially landed.