Geology was the science, specifically planetary science, involving the study of the natural landforms of a planet or other celestial body with a solid surface. One who studies geology was known as a geologist or exogeologist. Fields of geologic research included volcanology, mineralogy, geomechanics, and geochemistry. Geology was a common part of the Federation Starfleet's scientific portfolio and Constitution-class, Galaxy-class, as well as Intrepid-class starships had geological labs. (TOS: "The Cage"; TNG: "Pen Pals"; VOY: "Course: Oblivion")
In 1893, Samuel Clemens told numerous guests in a ballroom in San Francisco that geology had indicated that Human beings had been around for only a microscopic amount of time that the Earth had been in existence. (TNG: "Time's Arrow")
The geology on Terra Nova was comprised mainly of beresium ore. In 2151, Commander Trip Tucker told Captain Jonathan Archer that due to the geology on Terra Nova being "a little shaky", the Novans' numerous passageways in their tunnels and wells had collapsed. (ENT: "Terra Nova")
In 2152, not convinced that T'Pol had made up a story about her foremother T'Mir being the very first Vulcan to interact with Humans in the 1950s, Jonathan Archer said that she had visited Carbon Creek, where T'Mir had been. T'Pol remarked that as a scientist, she had also visited Yellowstone Park and Carlsbad Caverns, as she had an interest in geology. (ENT: "Carbon Creek")
In 2153, Gralik Durr, a Xindi-Arboreal, told Jonathan Archer that the Xindi's homeworld, Xindus, was a geologically unstable world during the Xindi Civil War and was eventually destroyed when the Xindi-Insectoids and Reptilians detonated large explosions beneath eight of the planet's largest seismic fissures. (ENT: "The Shipment")
In the Julian Bashir, Secret Agent holoprogram, Julian Bashir declared "Baccarat and geology are my life". (DS9: "Our Man Bashir")
In 2373, Worf told Jadzia Dax while they were vacationing on Risa that it was "nothing more than a rain soaked, geologically unstable jungle" without the planet's use of its weather control system and seismic regulators. (DS9: "Let He Who Is Without Sin...")
In 2375, a Silver Blood USS Voyager copy of Tuvok told his duplicate crew mate Chakotay that they picked up silicate from a comet in the Podaris sector nearly a year before. Chakotay replied that the silicate had been stored in the ship's geology lab since then. (VOY: "Course: Oblivion")
In 2377, B'Elanna Torres asked Icheb if he would be interested to join her on the holodeck for rock climbing. Icheb replied that he had some interest in geology, but Torres insisted that it was not about rocks, but rather the climb. (VOY: "Nightingale")