What conditions found in volcanoes are favorable for diamond formation?

Explanation:

There are a number of scenarios where diamond formation is possible. The most interesting out of these is probably the formation of diamonds in the outer reaches of our solar system. NASA researchers have found very tiny pieces of diamonds in extraterrestrial bodies, which have formed either in space or in the mantle of some other planets.

Also, there do exist obscure places on our planet which are ideal for diamond formation. For example, diamonds were discovered in subduction zones where two different tectonic plates meet each other.