Brown graining in a natural diamond
Pictured below is a striking brown internal graining in a natural near-colorless diamond [1]Massi L. (2005) Studies of defects in brown and hydrogen-rich diamonds, PhD thesis, University of Nantes – France, 372 pages (PDF). Brown graining – made of one or more set(s) of brown planes parallel to the octahedron faces {111} – is present in some diamonds that have undergone post-growth plastic deformation [2]Fritsch E. (1998) Colour in Diamonds, The Nature of Diamonds, edited by George E. Harlow, American Museum of Natural History, pp. 23-47.
When seen under crossed polarizing filters those diamonds show a strong strain pattern (photomicrography below), typical for plastically deformed diamonds of octahedral growth [3]Hainschwang T. (2014) Diamants de type Ib: Relations entre les propriétés physiques et gemmologiques des diamants contenant de l’azote isolé, PhD thesis, University of Nantes – France, 413 pages.
To go further:
(literature the reader might be interested to read to get more technical information on the topic covered in this blog post)
- King J.M., Shigley J.E., Gelb T.H., Guhin S.S., Hall M., Wang W. (2002) Characterization and grading of natural-color pink diamonds, Gems and Gemology, Vol. 38, No. 2, pp. 128 – 147.
- Massi L., Fritsch E., Collins A.T., Hainschwang T., Notari F. (2005) The ‘‘amber centres’’ and their relation to the brown colour in diamond, Diamond & Related Materials vol. 14, pp. 1623 – 1629.
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