He into the lithosphere

Noble gases in diamonds have received considerable attention, both for clues to the conditions of diamond formation and preservation in the mantle, and because of the possibility that diamonds have retained ambient noble gases from the lower lithosphere and from early in Earth history. There have been many reviews on diamond formation in general more recent reviews include Haggerty (1999) and Navon (1999). Since Takeoka and Ozima (1978) reported that diamonds have sufficient He that isotopic compositions could be obtained, many studies have examined the variations recorded in diamonds of different locations and characteristics. 

There are several characteristics to consider in using diamonds as noble gas samples  

These therefore sample some of the thickest regions of the lithosphere and are from deeper than xenoliths from young alkalic volcanism. 

Therefore, there is potential for considerable production of radiogenic nuclides both in the kimberlite source region, and in the matrix surrounding diamonds after eruption. 

Takeoka and Ozima 1978 Ozima et al. 1983 Kurz et al. 1987 Honda et al. 1987), making them amenable for study. In particular, some diamonds are coated with an impure layer of varying thickness that is often rich in fluid inclusions and volatiles (Navon et al. 1988), including rare gases (Burgess et al. 1998). 

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