In this amazing photo we see a gigantic polished sphere of petrified wood approximately 12″ in diameter. According to Wikipedia:

Petrified wood is the name given to a special type of fossilized remains of terrestrial vegetation. It is the result of a tree or tree-like plants having completely transitioned to stone by the process of permineralization.
 
All the organic materials have been replaced with minerals (mostly a silicate, such as quartz), while retaining the original structure of the stem tissue. Unlike other types of fossils which are typically impressions or compressions, petrified wood is a three-dimensional representation of the original organic material.
 
The petrifaction process occurs underground, when wood becomes buried under sediment or volcanic ash and is initially preserved due to a lack of oxygen which inhibits aerobic decomposition. Mineral-laden water flowing through the covering material deposits minerals in the plant’s cells; as the plant’s lignin and cellulose decay, a stone mold forms in its place. [source]

 

If you’re interested in these works of art, you can find many available for sale online. Searches on Fossil Era and Etsy brought up a number of current and past listings. I was unable to find a source for the particular specimen above, and a reverse image search on Google and Tineye did not produce any leads either.