See the AMNH's vital statistics . When prospecting for diamond, good indicator minerals are red garnet and olivine. This is a fact. Primary deposits of diamond are only found in the intrusive, igneous rock type called kimberlite. Diamond is also found in lamproite deposits, see AMNH's kimberlite and lamporite .
Inclusions are helpful to identify the rock within which diamonds formed and the age of the diamond.
Although inclusions include garnet and diopside, the most common inclusion in diamond is diamond. This is a fact. Image taken from DeBeers History and Mining Image taken from DeBeers 11. Diamond was first mined in Brazil. Extensive diamond mining began in India.