Among the precious stones, the most extensive foreign trade during the Gupta age was that of :

The correct answer is Option 1: Diamonds.

During the Gupta period, often referred to as the Golden Age of Indian history, India maintained flourishing maritime and overland trade routes with the Roman Empire and Southeast Asia. While India was famous for various gemstones, Diamonds constituted the most extensive and lucrative item of foreign trade among precious stones.

• Economic Significance: Contemporary literary works like Kalidasa’s Raghuvamsa and Varahamihira’s Brihat Samhita provide detailed accounts of diamond mining and their categorization, indicating a highly organized industry.
• Global Demand: Indian diamonds were unparalleled in quality and were in high demand in the Roman markets. They were a primary export from ports like Bharuch (Barygaza) and Tamralipti.
• Comparison: While pearls (Option 3) were significant exports from South India, diamonds remained the premier luxury commodity from the Gupta heartland, fetching immense wealth in gold (Dinara) from foreign traders.

Thus, due to their high valuation and volume in international markets, diamonds were the most extensively traded precious stones during this era.