Since it was difficult to obtain and process tama (gems) in Japan (nephrite is harder than steel and can be processed only using a thread coated with the powder of a harder stone), white stones were mostly used instead of white gemstones in modern times even though they were still referred to as white gemstones.
玉は日本では入手しがたく、かつ加工も難しいので（軟玉も鉄鋼より硬く、硬い石の粉末をつけた糸などでしか加工できない）、近世では白玉と称しても多くの場合白い石をもって代用する。