Geosmin (/iˈɒzmɪn/ jee-OZ-min) is an irregular sesquiterpenoid, produced from the universal sesquiterpene precursor farnesyl pyrophosphate (also known as farnesyl diphosphate), in a two-step Mg2+-dependent reaction.[1] Geosmin, along with the irregular monoterpene 2-methylisoborneol, together account for the majority of biologically-caused taste and odor outbreaks in drinking water worldwide.[2] Geosmin has a distinct earthy or musty odor, which most people can easily smell. The geosmin odor detection threshold in humans is very low, ranging from 0.006 to 0.01 micrograms per liter in water.[2] Geosmin is also responsible for the earthy taste of beetroots and a contributor to the strong scent (petrichor) that occurs in the air when rain falls after a spell of dry weather or when soil is disturbed.[3]

Quick facts: Names, Identifiers, Properties, Hazards...
Preferred IUPAC name
Other names
(4S,4aS,8aR)-4,8a-Dimethyl-1,2,3,4,5,6,7,8-octahydronaphthalen-4a-ol; 4,8a-Dimethyl-decahydronaphthalen-4a-ol; Octahydro-4,8a-dimethyl-4a(2H)-naphthalenol
3D model (JSmol)
ECHA InfoCard 100.039.294
  • InChI=1S/C12H22O/c1-10-6-5-8-11(2)7-3-4-9-12(10,11)13/h10,13H,3-9H2,1-2H3/t10-,11+,12-/m0/s1 Y
  • InChI=1/C12H22O/c1-10-6-5-8-11(2)7-3-4-9-12(10,11)13/h10,13H,3-9H2,1-2H3 /t10-,11+,12-/m0/s1
  • O[C@]12[C@H](CCC[C@]2(CCCC1)C)C
Molar mass 182.307 g·mol−1
Melting point 78 to 82 °C (172 to 180 °F; 351 to 355 K)
Boiling point 270 to 271 °C (518 to 520 °F; 543 to 544 K)
Flash point 104 °C (219 °F; 377 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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In chemical terms, geosmin is a bicyclic alcohol with formula C12H22O, a derivative of decalin. Its name is derived from the Ancient Greek words γεω- (geō-), meaning "earth", and ὀσμή (osmḗ), meaning "smell". The word was coined in 1965 by the American biochemist Nancy N. Gerber (1929–1985) and the French-American biologist Hubert A. Lechevalier (1926–2015).[4][5]