Rough, uncut emeralds are worth less than their faceted counterparts, for a few reasons:
There is an exception to this for well-formed mineral specimens, but these are few and far between. Nature rarely makes ideally formed gems and finding them is like finding a winning lotto ticket.
Not every emerald is gem-quality. There are various grades of emeralds ranging from highly included, opaque material to the transparent material selected for gems. The emerald clarity ranges from opaque to translucent emeralds in carving-grade, translucent to semi-transparent in cabochon-grade, and lastly transparent in facet-grade. These grades also apply to other gemstones.
Cartier “Tutti Frutti” Bracelet
Emerald ID: E1591
Emerald ID: E6
The rarest, most desirable, and most expensive emerald material is always facet-grade (discounting any historical or celebrity ownership). There is also evaluation of the gem material according to the 4Cs of color, clarity, cut, and carat weight. Since we are discussing uncut emeralds, most of these factors cannot be precisely calculated. However, the color is the biggest drive of value in emeralds and can be evaluated before cutting.
Emerald green is also not a single color, but a range. Sometimes emeralds are more yellowish, or preferably bluish. High quality emeralds are usually pure green to bluish, since yellowish ones look very similar to peridot (a characteristically yellowish green gem). If they are visibly yellowish, it is only in the faintest amounts.
Emerald ID: E1246
Weight: 3.11 Carats
Emerald ID: E904
Weight: 2.03 Carats
Emerald ID: E1587
Weight: 1.16 Carats
Aside from the value of the gem material itself and processing costs, other variables for price include international shipping, insurance, customs, etc. There are also issues with various gangs and corrupt officials in South America using forced labor in unproductive emerald mines. Hence certification that the emeralds were legally mined is very important in the international market.
One stunning example of this is the Bahia Emerald. It is the largest emerald ever known at 752 pounds, though the quality of the emeralds is very low. It has been in the midst of ownership disputes since 2008. All the details of this are a convoluted, scheming mess that has been making heads spin for decades. The disputes were supposedly settled in 2015, until the Brazillian government claimed the emerald was illegally smuggled out of the country and is rightfully theirs. Keep in mind that happened right before the case had been settled.