The black coloration of the summit rock is the accumulated product of billions of microorganisms — specifically, a community of cyanobacteria, other bacteria, algae, fungi, and lichens collectively known as a biological soil crust or cryptobiotic crust — that have been growing on the rock surface for a very long time.

These microorganisms form a dark, thin film on the rock surface that gives it the characteristic black appearance.

The film is alive — it contains photosynthetic organisms that capture energy from sunlight and organisms that can fix atmospheric nitrogen.

It is an important part of the summit nutrient cycle, as the nitrogen-fixing microorganisms convert atmospheric nitrogen into forms that can be used by plants, partially compensating for the nitrogen poverty of the summit soils.

The black biofilm is also extremely fragile.