Primary crystal

&

face morphology of natural diamonds can reflect their geochemical characteristics and forming conditions at deep mantle to some extent

and secondary micromorphology superimposed in magmatic transit to surface and in stream transportation can be used to explore their postforming experience and the remaining time of diamonds on earths surface. This paper presented the types based on infrared spectrometer analysis

crystal

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face morphology of 297 diamonds from modern deposits along Yuan river basin in Hunan. The  results show that 282 diamonds belong toⅠaAB type

3 diamonds areⅠaB type

and 5 diamonds are Ⅱa type. Morphology analysis results show that Hunan diamonds have clear and well preserved surface erosion possibly reflecting a rapid magma transit from far deep to the surface. Triangular and occasional hexagonal etch pits are common on crystal face (111) of some diamonds indicating a forming environment of oxidizing H

2

Orich metasomatic fluid/melts in the mantle during diamond resorption events. One diamond shows extraordinary crystalline form like a diver helmet which was only found in Kalimantan diamonds. Hunan diamonds show clear similarity with Western Australia diamonds in crystal morphology

nitrogen contentbased diamond type

inclusions and carbon isotopes. These evidences suggest possible genetic relationship between Hunan diamonds and Western Australia diamonds

and therefore Hunan diamonds were formed not earlier than the Paleoproterozoic

and more likely related to the subduction in Neoproterozoic.