Diamonds are found in kimberlite and lamproite pipes, which are volcanic structures formed deep within the Earth's mantle. These pipes bring diamonds, formed under intense pressure and heat, to the surface.

Here's a breakdown:

* Kimberlite pipes: These are the most common source of diamonds. They are vertical, pipe-shaped structures formed by explosive volcanic eruptions. Kimberlite is a rock type containing a variety of minerals, including diamonds.

* Lamproite pipes: These are less common than kimberlite pipes but also contain diamonds. Lamproite is a type of volcanic rock that is richer in potassium and magnesium than kimberlite.

Diamonds are also found in alluvial deposits, which are formed by the erosion and transportation of kimberlite and lamproite pipes. These deposits can be found in riverbeds, beaches, and other areas where the original pipes have been eroded away.

Here are some of the major diamond-producing countries:

* Botswana

* Russia

* Canada

* Australia

* South Africa

* India

* Brazil

* Democratic Republic of Congo

So, while diamonds are formed deep within the Earth, they can be found in various locations, both primary sources (like kimberlite pipes) and secondary sources (like alluvial deposits).