You need to use other radioactive decay schemes (e.g., uranium-lead) to date inclusions in diamonds.We find diamonds as inclusions in the (rather ordinary looking) volcanic rock known as kimberlite.
NOTE: The kimberlite magmas that carry diamonds to the surface are often much younger than the diamonds they transport (the kimberlite magma simply acts as a conveyer belt! It is probable that kimberlite lavas carrying diamonds erupt at between 10 and 30 km/hour (Eggler, 1989).
Within the last few kilometers, the eruption velocity probably increases to several hundred km/hr.
The explanation is found in the fact that in diamond the carbon atoms are linked together into a three-dimensional network whereas in graphite, the carbon atoms are linked into sheets with very little to hold the sheets together (thus the sheets slide past each other easily, making a very soft material).
How many grams do you need to mine to get 5 grams of diamonds? But only 20 % are gem quality (80 % of these are sold in a "managed selling environment") and the remainder are used for industrial purposes (this material is known as "bort" or "carbonado" (carbonado is finer)).
The volcanic magma conduit is known as a kimberlite pipe or diamond pipe.
Inclusions used for dating are around 100 microns in diameter (0.1 mm).