Some very interesting reading on diamonds can be found in the publication, Gems & Gemology, published by the Gemology Institute of America (GIA). I've got issues dating back to 1934, but there's an interesting article in the Spring 2002 issue, titled "Understanding the Relationship of Pink and Red Diamonds in GIA's Color Grading System".
The following extract from that report highlights the fact that our recent find is likely to be very rare indeed. For those who may not be aware, Type II diamonds are more valuable than Type I. I'm sorry I can't give you a link to the article as it's from page 12,262 of a PDF document on my hard drive:
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