There are four types of dilithium chamber that have been shown to date. One was that of the Template:ShipClass starship, though exactly which component of the reactor was the chamber itself was never disclosed.
The second was used on board the original configuration of the Template:ShipClass. It was a squat cylinder with a blunt domed top in the center of main engineering. The dilithium crystals were housed in a framework that rose out of one side of the chamber.
The next was the columnar "swirl" chamber, as shown in the Constitution-class refit and the Template:ShipClass. Backstage information, including interviews with Rick Sternbach, indicate that in this model of chamber, the entirety of the column is the reaction chamber, which is lined with a layer of dilithium to moderate the reaction.