Jennite is a calcium silicate hydrate mineral of general chemical formula: Ca9Si6O18(OH)6·8H2O.

[3] It typically occurs as vein and open space fillings as a late mineral phase.

They named it in honor of its discoverer: Clarence Marvin Jenni (1896–1973) director of the Geological Museum at the University of Missouri.

[3] In contrast to the first analysis made by Carpenter, jennite was found to not contain appreciable amount of sodium when the Crestmore specimen was reexamined.

[6] Jennite is often used in thermodynamical calculations to represent the pole of the less evolved calcium silicate hydrate (C-S-H).