The discharge crystal was a part of Federation phaser rifles.

The efficiency reading on the discharge crystal of a phaser rifle manufactured by the Romulans was well above Starfleet specifications. Starfleet's most efficient discharge crystal typically fired with 86.5% efficiency, whereas the Romulan copy fired at 94.1% efficiency. This was one of the hints that finally revealed that the rifle was a forgery. (TNG: "The Mind's Eye")

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