The history of Indian jewellery cannot be considered complete without a study of the gems themselves. India has been one of the greatest trading centres for gems and other precious stones throughout the ancient and medieval periods of Indian history. The vast mass of Indian literature both, indigenous and foreign, have references to Indian gemstones. Subsequently, all this knowledge was compiled into a science called Ratna-Pariksha.]
The Arthasastra of Kautilya, the Kamasutra of Vatsyayana, the Brihatsamhita of Varahamihira and the Ratna-Pariksha of Buddhabhatta are the authoritative texts from the past. The earliest text in this connection is, no doubt, the Arthasastra of Kautilya and then, the Kamasutra of Vatsyayana who included gemology among the sixty-four Anga-Vidyas or subsidiary arts.
The Ratna-Pariksha section in the Brihatsamhita of Varahamihira, an astronomer, and the Ratna-Pariksha of Buddhabhatta, a Buddhist scholar, are later works datable to the sixth century AD and both have referred to earlier authorities.

The Brihatsamhita of Varahamihira has listed twenty-two varieties of stones in the category of ratnas (gems) without differentiating between the major gems (maharatna) and minor gems (uparatnas), a classification which seems to have developed later.

The twenty-two ratnas are:
Vajra (diamond), Indranila (sapphire), Marakata (emerald), Karketana (chrysoberyl), Padmaraga (ruby), Rudhirakhya (carnelian), Vaidurya (cat’s eye), Pulaka (garnet), Vimalaka, Raja-mani, Sphatika (rock crystal), Sasikanta (moonstone), Saugandhika (a variety of sapphire), Pushparaga (topaz), Brahmamani, Jyotirasa, Sasyaka, Mukta (pearl) and Pravals (coral).

Of these, the Ratna-Pariksha section of the Brihatsamhita deals with four gems in great detail - diamond, pearl, ruby and emerald. The rest like sapphire, chrysoberyl, garnet and so on are mentioned only in passing.