also: こうぎょく
noun
Mineralogy term for the gemstone topaz. Both readings refer to the same mineral.
黄玉は11月の誕生石です。
Topaz is the birthstone for November.
この指輪には大きな黄玉がはめ込まれている。
A large topaz is set in this ring.
Katakana loanword for topaz, more common in everyday contexts. 黄玉 is the kanji term used especially in mineralogy or traditional contexts.
From 黄 (yellow) + 玉 (gem, jewel), referring to the typical yellow color of topaz. The reading おうぎょく uses the on'yomi of both characters; こうぎょく is an alternate on'yomi reading.