How much diamond is in the mantle?

Excuse me, could you please elaborate on the quantity of diamond present within the mantle? I'm particularly interested in understanding the extent of diamond distribution and abundance in this geological layer. Could you provide any estimates or figures that might help me visualize the scale of this phenomenon? Additionally, I'm also curious as to the methods used to determine such measurements and whether there are any ongoing research efforts in this area. Thank you in advance for your insights and clarification.