How do you know what techniques Al-Biruni used to identify gemstones?

Al-Biruni, a renowned Persian scholar of the 11th century, documented his techniques for identifying gemstones in his work "Kitab al-Jamahir fi Ma'rifat al-Jawahir" (The Book of Precious Stones). He employed various methods, including physical characteristics like color, hardness, and specific gravity, as well as optical properties such as refractive index and transparency. His meticulous observations and experiments laid the groundwork for gemology, highlighting his scientific approach to the study of gemstones.