Records show from the 8th to the 16th century, the gemstone trade routed rough Indian stones by land and sea through Venice, Lisbon, and the Netherlands. In the 17th century, as the presence of the British in India increased, the East India Company began to dominate the export of diamonds from India.
Rough diamonds were routed through London and circulated from there to other cities, such as Amsterdam, Antwerp, and Paris, all of which were cutting centers that specialized in faceting gemstones into table, rose, brilliant, and other cuts. By adding more facets, lapidaries were able to unlock even more brilliance and "fire" (the rainbow of spectral hues) within the gemstone.
Some diamonds were mined in the Golconda region of India. A 14th-century atlas made in Mallorca illustrates the Valley of the Diamonds as neing a region in India. The crevasse is shown as being full of snakes, and two figures nearby slice red flesh to attract a vulture flying overhead. The mythical geography of the Valley of the Diamonds was also used to represent the region of India in several illustrated texts reaching as far as the Ottoman Empire, as seen in a 16th-century world history, the Maṭāli˓ al-sa˓āda wa manābi˓ al-siyāda.
Europeans have long associated diamonds with the virtues of purity and steadfastness, because of their clarity and hardness (the word "adamant" stems from the same Latin root as "diamond").
As early as the 16th century, rulers in the German provinces incorporated the stones into their insignia; Count Palatine and Duke of Bavaria Johann Casimir, for example, incorporated a ring set with a point-cut diamond into his impresa. Even his motto, constanter et sincere, references the virtues associated with the stone.
A London jeweller by the name of Delles obtained a big beautiful green diamond at the end of the 17th century, and cut it into a modified a pear-shaped brilliant cut.
After many years trying to find a suitable buyer, he sold "The Dresden Green" to Augustus II. He paid so much for it that Frederick II of Prussia ("Frederick the Great") complained that "for the siege of Brünn [the capital of Moravia] the king of Poland was asked for heavy artillery. He refused due to the scarcity of money; he had just spent 400,000 thaler for a large green diamond." (At the time, the exorbitant sum would have been worth about four tons of gold.)
So Charles I wasn't the only king to invest in art and short-change the army!
For more info on the Dresden Green, see https://www.metmuseum.org/blogs/now-at-the-met/20…
For information about the Indian diamond fields, see https://www.metmuseum.org/blogs/now-at-the-met/20…