Mantle

The mantle was one of the interior layers of planets and stars. On planets, it was found between the crust and the outer core.

Terra 10 was a Class M planet and its mantle was entirely crystalline, including a rich abundance of dilithium. 

While the USS Enterprise (NCC-1701-D) was attempting to help the planet of Penthara IV by drilling into the surface with phasers, the drilling destabilized the stable tectonic plates and the mantle began collapsing around the bore sites, causing several volcanic outbreaks and severe earthquakes. 

The Atlantis project on Earth was working to accelerate the build-up on the underside of the mantle without increasing the stress on the tectonic plates. 

In 2371, the Obsidian Order and Tal Shiar combined task force had sufficient to obliterate the crust of the Founders' homeworld in one hour, and the mantle in five. 

While lost in the Delta Quadrant aboard the Delta Flyer, Tom Paris, Samantha Wildman, and Tuvok discovered a Class M planet with a benamite mantle and several active volcanoes. 

The planet Sikaris had a mantle of tetrahedral quartz twenty kilometers thick. The crystalline structure of the planet's mantle served as an amplifier for the Sikarians' spatial trajector technology. 

According to an Alpha Hirogen hunter, at least one collapsed star in the Delta Quadrant had a neutronium mantle. The hunter claimed to the crew of Voyager that he tracked a silicon-based lifeform through this mantle.