Petrichor ~ essence of Rock, is derived from the Greek words Petros (stone) and Ichor (fluid flowing in veins of gods). It means the pleasant smell of the first rain after a long period of warm dry weather.

Two Australian researchers discovered that this fragrance is an oily essence that comes from rocks or soil that are often clay-based. It’s a complicated set of at least 50 (!) different compounds, like a perfume. During dry spells, the vegetation gives off the oils, which is absorbed by the rock surface and soil particles. When the first rains begin, these fragrances are released into the air, and this is what we smell.
Pretty amazing, isn't it?