What's the Difference between Jadeite & Omphacite Jade?
Jadeite and omphacite are members of a large group of rock-forming minerals called pyroxenes. Members of the series, while all related to one another, are actually different minerals based on changes in chemistry and/or structure. What this means is that sometimes the borders between members can become indistinct—not from a mineralogical point of view, but from a practical perspective.
What did the Research says?
Researchers from GIA started collecting Raman spectra on every piece of jade that came through the lab and found that while most pieces were indeed jadeite, a surprising number were omphacite. Pieces whose gemological properties were absolutely identical to jadeite—appearance, colour, texture etc were identified as omphacite. Even some fine-quality pieces with the appearance and characteristics of Burmese jadeite fell into this category.
Omphacite Jade which has also been endorsed by the Chinese/Hong Kong mineralogists who have accepted it as 'Fei Cui', a term used to describe finely textured jadeite.
Omphacite Jades are not equivalent to fake/imitation jadeites.
Referenced from GIA: