pet·ri·chor 
(pĕtrĭ-kôr′)
(pĕtrĭ-kôr′)n.
1. The distinctive smell given off by earth, rock, or pavement at the beginning of a rain after a period of warm, dry weather.
2. The organic compounds that produce such a smell.
[PETR– + ICHOR (coined in 1964 by Isabel Joy Bear and Richard Grenfell Thomas, Australian geochemists).]