Final answer:
Lichen promotes the breakdown of hornblende granite through biological weathering, a process involving a symbiotic relationship that leaches nutrients and initiates rock breakdown leading to soil creation.
Step-by-step explanation:
The growth of lichen on the surface of hornblende granite and its contribution to the breakdown of the rock is an example of biological weathering. Lichens, which are a symbiotic relationship between a fungus and a photosynthetic organism like an algae or cyanobacterium, leach nutrients from rocks, initiating the breakdown process that leads to soil creation. This form of weathering is fundamental in the early stages of ecological succession, where living organisms start to inhabit a previously uninhabitable area.
Weathering can be either physical, caused by mechanical processes like freezing and thawing, or chemical, influenced by reactions such as the acidity of rainwater or the presence of air pollutants. The presence of water is a significant factor in both forms. Biological weathering, like what occurs with lichens, can be considered part of chemical weathering since it involves the production of substances that chemically interact with the rock minerals.