Crust
The crust was the outermost layer of a planet. It surrounded the mantle.

The crust of a planet was often subject to seismic disturbances. Seismic regulators were used to control this activity. (; )

Most of the eisillium deposits on Archer's Comet were twenty meters below the crust of the comet. ()

Terra 10 was a planet with a crust that was entirely crystalline. ()

In 2365, Wesley Crusher and a team of geologists  that a planet had become unstable because unusually high levels of dilithium in the crust had formed a matrix which created a piezoelectric effect that was tearing the planet apart. This effect translated geothermal energy into mechanical force. ()

In 2371, thirty percent of the crust of the  was destroyed by weapons fire from starships above during the Battle of the Omarion Nebula. ()

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Geology