Etymology: From the Greek petri (meaning “stone”) and ichor (the mineral found in the blood of the gods of Greek mythology). The word was coined by two mineralogist, Isabel Bear and R. G. Thomas in an article for Nature magazine in 1964. In their article, “Nature of Argillaceous Odor”, Bear and Thomas describe the process of how that pleasant, distinctive scent is released into the air. During summer, certain plants release oil (in order to prevent seeds from germinating under duress) that is absorbed by clay-based rocks and soil. When it rains, these oils along with geosmin (a metabolic by-product of Actinobacteria), are released into the air, creating that fragrant scent.
Anthropologist Diana Young reports that for the Aboriginal peoples, who manufacture their own petrichor perfume out of plant and animal fat, the scent is not only cleansing and protective, but it also links the current generation to past generations.
For further reading: scientificamerican.com/article.cfm?id=storm-scents-smell-rain