gems, Arabic mineralogy, al-Biruni, specific gravity, density

Khanikoff presents an extensive analysis and extracts from al-Khāzinī’s twelfth-century Arabic Kitāb Mīzān al-Ḥikma [Book of the Balance of Wisdom], an important medieval treatise on balances, hydrostatics, and the determination of specific gravity. The work describes the construction and operation of highly sensitive balances, methods of weighing substances in air and water, and procedures for determining the specific gravities of metals, minerals, precious stones, and liquids. Of particular gemological importance are numerical data for precious stones and minerals—including ruby, emerald, diamond, sapphire, and quartz—and discussions of their identification by density. Khanikoff also examines al-Khāzinī’s reliance on earlier Greek and Islamic scientific traditions, particularly Archimedes and al-Bīrūnī, whose experimental determinations of specific gravity are preserved in the treatise. The paper provides an important nineteenth-century Western account of medieval Islamic achievements in quantitative mineralogy and demonstrates the sophisticated application of hydrostatic weighing to the examination and identification of gemstones centuries before the development of modern gemology.