New word from Australia's CSIRO

Petrichor: The name of an oil that’s released from the earth into the air before rain begins to fall. Hence, the distinct scent of rain in the air.
From the Greek “petra” (stone) and “ichor”, the ethereal blood of the gods in Greek mythology.
For more, see this IFLS article or Nature of Argillaceous Odour (metered paywall) by I J Bear & R G Thomas of CSIRO Division of Mineral Chemistry, Melbourne, Australia.