Natural Emerald is the green variety of the Beryl mineral. The green color of this Gemstone recalls lush landscapes, such as those of Ireland, nicknamed the Island of the Emerald.
Beryl measures 7.5 in the Mohs scale of hardness and its Specific Gravity is about 2.72.
There are so many legends surrounding this Gem. Until a few centuries ago, it was believed that fishermen and sailors could protect themselves from the dangers coming from the sea only by wearing a Emerald set in a necklace.
Natural Emerald Refractive Index is normally 1,577-1,583, either in case it is filled, or in the very rare case it is not. Instead, Synthetic Emeralds generally have a lower Refractive Index compared to natural Emeralds. But beware: it is absolutely not enough just the Refractive Index test to separate them. In fact, sometimes Synthetic Emeralds have the exact same Refractve Index of the natural Emeralds, so it is necessary to do other tests and above all it is mandatory to observe the Emerald inclusions under a microscope.
The Flash effect is the telltale signal revealing the fracture filling treatment in these Gemstones.
The Flash Effect is visible in this link when the Emerald is tilted.
Over 90 percent of natural Emeralds are treated with oil or resins or polymers. Opticon is often used to fill the typical fractures reaching the Emeralds surface. This treatment hides fractures and temporarily improves the appearance of the Precious Gemstone. In fact it improves Color and Clarity.
The three fracture filled Emeralds categories are: Minor, Moderate and Significant, depending on the amount of oil, wax or polymers (eg Opticon) present in these Precious Gemstones. There are guidelines recognized by 20 gemological laboratories around the world. But we have not yet reached a complete agreement about the boundary between the three levels of fracture filling treatment in the Emerald.
Cleaning the Emerald with fractures filled with Opticon, or even worse oil, could be a mistake. In fact it can happen that the ultrawaves emitted by the machine remove the oil, replacing it with the dirty fluid present in the machine. The latter could dry up and settle between the fractures, thus ruining irreparably the Gemstone.
A very special Emerald variety is the Trapiche Emerald, from Colombia and discovered in the legendary Muzo mine. Trapiche Emeralds are Emeralds having 6 spokes drawing a hexagonal circle. They usually consist of a green Crystal in the form of a hexagonal prism with 6 darker regrowth rays containing carbon. From the center of the crystal, the 6 rays move towards the six edges of the crystal. Finally a Beryl and Feldspar mixture fills the radial spaces.
The Emerald green color is due to Chrome trace elements, but Vanadium can give the green color to these Beryls. When Beryl occurs:
blu is called Acquamarine,
colorless Goshenite and
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