In which country pure and excellent diamonds are found?

A 'pure and Excellent' diamond, in other Words, one that is potentially flawless, of highest-jewelry grade colour (D) and one that can be cut with a superior cut can be found in many countries, notably, India, several African countries, Canada, Australia and potentially other places.

At auction, the types of diamonds that usually fetch the highest prices are those classified as type IIa stones, which are "...almost or entirely devoid of impurities..." Many large famous stones, the Cullinan and Koh-i-Noor are type IIa stones -- from South Africa and India, respectively. Also, Australia produces many type IIa stones.

Read more about types of diamonds, below.