These are polished spheres carved from real stromatolites! They would make for wonderful display items or gifts!
Stromatolites are natural layers formed by photosynthetic cyanobacteria (also known as blue-green algae).
Though they have become rare in the modern era, the fossil record shows that they were far more abundant in the past - especially in the Precambrian.
Worldwide shipping is available and they measure an average of 2.5" diameter (400g).