You can purchase diamonds in most any city in the world. There is no 'city' where diamonds are mined, however.
Most jewelery stores in most cities in Europe sell diamonds.
Diamonds are found in diamond mines in Africa, unless you're shopping for diamonds. If the later, you can visit any jewelery story in any city in Africa that sells diamonds and find them there.
Greenland is not known for its raw diamonds. You can find a finished, cut and polished diamond to buy, however, in most any jewelery store in a Greenland city.
Diamonds are not found in a great many different places. Diamonds are not found floating in the ocean for example.
No, no natural diamonds are found in New Zealand.
Diamonds are commonly found in volcanic pipes.
Diamonds are found below level 16 of the world.
The diamonds themselves are, well, diamonds. They're found mixed in with other rock, though.
Coal and diamonds are both forms of carbon.
Diamonds are found on every continent except Antarctica and Europe - so yes, diamonds are found in India.
Diamonds are continuously being found around the world, so there is no specific "last time" that they were found. The mining of diamonds happens on an ongoing basis in various countries where they are naturally occurring.
Diamonds are found on every continent on earth except Europe and Antarctica.