rare treasure
鈺 centers on a precious object of exceptional value: a rare treasure, often implying something made of metal or jade.
鈺 combines 金 (metal) and 玉 (jade), suggesting a precious object made of metal or jade. The exact historical development is uncertain, but the component combination fits the meaning of a rare treasure.
Picture a rare treasure made of gold (金) and jade (玉) combined into one precious object: 鈺 is a rare treasure.
For ギョク, imagine a rare treasure so valuable it makes you gyak (a made-up sound like 'gyak') with surprise: gyak -> ギョク, and the treasure is 鈺.