This is a unique stromatolitic form I first saw only recently. The sphere-shaped bacterially formed ball (often called an algal ball) surrounds the still intact host rocks upon which the colony grew in ever-expanding bands. Such forms are often called Oncolite, and are typically found in ancient lakes.

Interestingly, one side of the large rock that would have been unexposed shows no growth. This specimen has been cut along one traverse plane and highly polished to show the intricate detail, while the remainder remains in its natural form.

Of further interest from a scientific perspective is the young age. This Cretaceous stromatolite was formed long, long after stromatolite-building organisms had to compete with other life forms, and hence had become uncommon on earth similar to modern times. The bacteria that formed this fossil had remained little changed during the preceding 3500 million years, dwarfing the short time period that dinosaurs walked the earth and then quickly disappeared.

This is a very unique and desirable specimen.