Ogri

The Ogri are a species of silicon-based creatures native to Ogros. They look like large, glowing rocks, usually taller than a human but irregular in shape. They are large, slow and heavy, sometimes weighing as much as 3.5 tons, but they can take a lot of damage, both energy based and physical. Like other silicon-based lifeforms, they break down into grit when killed. They feed on various types of proteins, which are common on Ogros. When on Earth, the Ogri had to rely on the globulin in blood, which they could absorb by touch. Ogri were not shown to communicate and did not show any signs of intelligence.

Cessair of Diplos took three Ogri from Ogros, which she used for protection and to impress the humans of Earth. These Ogri used to wait with the Nine Travellers until they were awoken by Cessair or her followers. (DW: The Stones of Blood)