Before we begin, I wish to specify that this video will be an overview of commonly used lightsaber crystal types within Legends Continuity, namely Adegan crystals, Ilum crystals, and Synthetic crystals. Unique crystals, such as Hurrikane amethysts or Durindfire gems, will be discussed in a follow-up video. With all of that out of the way, the first question that must be answered is "What is a lightsaber crystal?" Obviously, lightsaber mechanics are based on setting-specific psuedoscience, so check your scientific criticisms at the door.
The lightsaber crystal is used to convert energy from the lightsaber's internal power cell into the plasma arc waves that compose the lightsaber blade, the properties of the crystal determining the weapon's performance and handling. The ideal number of crystals is generally considered to be three, one primary crystal as the energy converter, and two focusing crystals that fine tune the blade. However, most lightsabers were fitted with only two, and there are numerous examples of weapons that employ only a single crystal doing double duty.