There is ongoing discussion among academics over the nature of the Nimrudlens, a piece of rock crystal unearthed by John Layard in 1850, in the Nimrud palace complex in northern Iraq.

• 有关尼姆德透镜的问题上，有一场学术性的争论。那是1850年间，约翰莱亚德在伊拉克北部的尼姆德宫殿遗址发掘的一块水晶头的石头。