Some Learning, page-7

So far I've found one scientific paper that is saying TypeIIa diamonds are lower mantle diamonds. They are rare making up 1–2% of all natural diamonds (1.8% of gem diamonds).

Also I didn't know it before but there is a very rare and very valuable TypeIIb diamond which only makes up about 0.1% of all natural diamonds. In addition to having very low levels of nitrogen impurities (comparable to TypeIIa's) theType IIb diamonds contain significant boron impurities. The absorption spectrum of boron causes these gems to absorb red, orange, and yellow light giving Type IIb diamonds a light blue or grey color, though examples with low levels of boron impurities can also be colourless.

Imagine if one of these showed up at Lulo.

Eshmun