AGATE, A MULTICOLOURED gemstone, is known as manao 瑪瑙 in modern Chinese.Zhang Hongzhao 章鴻釗 (1877–1951), a Chinese pioneeringgeologist, along with his colleagues, laid thegroundwork for the first national geographicalsurvey of China. One of his greatest geologicalcontributions was Shiya 石雅, a thorough study of the rocks,fossils, and metals known in Chinese literature. InShiya, Zhangidentified seventeen ancient rock terms from pre-Qintexts as agates, including two well-known terms:qiong 瓊 and chiyu 赤玉. The word manao, however, did notappear until the Later Han period.

Considering that there are over eighty kinds of agatein the world, a number of varieties might haveexisted in Chinese documents or society underdifferent names. How manao entered the Chinese lexicon andhow it gained popularity in Chinese culture bringour attention to the third century, when Buddhismand other foreign cultures arrived, and began toconverge with Chinese culture.

Manao, written as 瑪瑙 or馬瑙, appears thirty-five times in five sutrasproduced between the Later Han and Wei periods(Table 1). Manaoappears either as a symbol of a wealthy state suchas in Anabindi Hua qizijing and Xulaijing, or as one of the Seven Treasures,such as in Zhangzhezi zhijing, Wuliangqingjing pingdengjue jing, and Wuliang shou jing. In eithersymbolic form, this precious stone, along with otherprecious substances, attests to the connectionbetween its religious or spiritual status andeconomic, political, or religious power, as duringthe Middle Period of Indian Buddhism (0–500 ce) richmerchants were patrons and the target audience ofrising Buddhist doctrines.

These early Buddhist sutras, however, still did nottell us why the agate was called “horse brain.” Theexplanation within Buddhist writings came muchlater. Kuiji 窺基 (632–682) explained that the colourof the agate or 遏濕摩揭婆 resembles that of a horsebrain. According to Hui Lin 慧琳 (737–820), the agatewas called aśmagarbhain Sanskrit [阿濕摩揭婆], which means horse brain. Theagate's true name in Sanskrit, however, might begomedaka. Somescholars assert that aśmagarbha was invented to account forits Chinese name.