鋼こう玉ぎょくこうぎょくMeanings1nouncorundummineralogyMineralogy term for the crystalline form of aluminum oxide; includes ruby and sapphire varieties.鋼こう玉ぎょくは非ひ常じょうに硬かたい鉱こう物ぶつで、ルビーやサファイアも鋼こう玉ぎょくの一いっ種しゅです。Corundum is a very hard mineral, and ruby and sapphire are also varieties of corundum.
