The diamond Cognac is a variety of brown diamond of color.
Its color is caused by a plastic deformation. It is a deformation in the crystalline structure of the diamond that appears in the form of disturbance in the alignment of the atoms of carbon and which gives a form "waved" in the structure instead of right.
To know more about the mineralogy of the diamond Cognac, to see mindat.org ->
See the article on the Diamant
