Color, quality and size matters A primer on emeralds:
https://en.wikipedia.org/wiki/Emerald
Previous discovered occurences in Canada (Yukon) were close to surface and subjected to frost cycles, making the emeralds fracture and too small to be of the most desirable quality. The Yukon occurences have been abandoned.
This discovery was in a drill core, hopefully below the influence of temperature change.
According to the NR:
"the crystals are beryl and that the dominant chromophore is chromium with essentially no vanadium."
The highest quality emeralds have a light emitting effect due to the presence of chromium and the absence of other common impurites like vanadium. It is a good thing.