Optical studies have been made of the microstructures on the natural faces of diamond obtained from Panna mines, India. The trigons, the block pattern and the ring cracks have been observed to exist simultaneously on the natural faces of a large number of crystals. From the observations made it is conjectured that the Panna diamonds might have been subjected to solution in nature, and therefore the trigons along with the block pattern and the ring cracks might have been formed in this manner. On the natural face of one crystal rows of broken trigons have been found, and an exactly similar pattern has been produced in the laboratory by etching the octahedral face of calcium fluoride in nitric acid solution.

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