Grading and evaluating gems:-
Grading and evaluating gems can begin before they are extracted
from the ground. Certain areas within some gem deposits are known to yield more
or better-quality gems. material, and thus are mined first. Only a small
proportion of What is recovered is of gem quality, and this is confirmed. Sorted
to extract the gem material any gemstone-quality Roughs discovered are then
carefully evaluated for color, clarity, and size. as well as size Even if much
of the selected material remains, uncut if it is too small, oddly shaped, or
otherwise does not fit and does not meet current market demand Cutting is
costly, and at this early stage, grading is time-consuming and meticulous is
critical. To be sure, the cutter will make the final decision about what is
cut, but the more evaluation and grading that occurs before gems arrive at the
cutter's workshop, the better.
Non-gem quality
The specimen shown here is ordinary zoisite, and it is
representative of almost all zoisite material. It's hazy, and even when it is
well crystallized but not of gem quality. Until the discovery of tanzanite,
zoisite was the most valuable mineral. Only a small number of gem-quality
variants exist. There was a known amount of gem-quality zoisite.
Mid-gem quality
Because tanzanite is a relatively uncommon stone, even
medium-quality gems are valuable enough to facet. In more common stones, such
as amethyst, a mid-quality rough is rarely faceted because the cost of cutting
it would exceed the final value of the finished gem.
Superior quality
Only a small percentage of even the finest gemstone rough is of
excellent quality. Both the rough and cut stones in this tanzanite sample are
clearly of greater quality than the mid-class grade.
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