Minerals and Metals in Ancient India v2.c43.s3.t2.12

v2.c43.s3.t2.12

Like blue to yellow transition, sapphire was known to have blue to red transition also, and such reddish blue coloured corundum samples could be called either sapphire or ruby. As a matter of fact, the Arabs guessed (without any scientific knowledge) that sapphires and rubies belonged to a transitional single group of gem mineral, and they called this *Yāqūt* which, according to Al-Afkānī, occurred in seven varieties. (Sarma, 1984:61; Wiedemann, 836-40) Both ruby and sapphire crystals, specially the dark coloured ones, are dichroic, i.e., appearing differently coloured when viewed through mutually perpendicular axes. The famous ‘Sapphire Marveilleux’ appears blue by day and red amethystine by night (*Maṇimālā*, p. 459). Sapphire with a dash of red has been known as *tittibha* (*MM*, 423) A deep blue gem dashed with red was known as *nīlāṅga* or violet-ruby (*Maṇimālā*, part 2, pp. 514-15).