Dilithium crystals

Crystals in the frame

In 24th century starships, the dilithium articulation frame held the dilithium in alignment with the colliding matter/antimatter stream and was housed inside the matter-antimatter reaction assembly. The frame was housed behind the dilithium chamber hatch. (TNG: "Skin of Evil", "The Drumhead")

In 2366, Geordi La Forge, along with a holographic program that included Doctor Leah Brahms' personality, made an experimental field modification to the USS Enterprise-D frame which re-oriented the crystal to adjust the lattice structure. This was contrary to Starfleet regulations, but it worked in a crisis situation. Later, Doctor Brahms inspected the Enterprise's frame in 2367 and discovered the modification, surprised to see an innovation that would be in the next class of starship. La Forge did not take full credit. (TNG: "Booby Trap", "Galaxy's Child")

The frame suspended the dilithum in the reaction chamber using a field effect to keep the crystal faces in alignment with the matter/antimatter streams. The correct alignment of the crystal faces and planes maximized the efficiency of the plasma conversion that took place. By the 2360s, the theta-matrix compositor was integrated with the articulation frame, allowing recrystallization to take place in the warp core with the core online. (TNG: "Relics")