What is Emerald Gemstone?

 Rough Emerald                                             

Cut and Polished Emerald

By Eng.Gilay Shamika: 

Senior Engineer and Gemologist at TMAA

Emerald name comes from Greek word meaning green. Before, Greeks called all gemstones with green color Emeralds until when gemological knowledge categorized other green colored gemstones according to their refractive index.

Emerald being among the ‘big four’ gemstones which are Ruby, Sapphire, Tourmaline and Emerald itself, it assumes higher price as well. However, compared to other big four gemstones, Emeralds are the gemstones which are rarely found without inclusion and fractures. Most of Emeralds are found with fractures and inclusions. Therefore, there is tolerance in the market for Emeralds grades, that is fracture filling and inclusions into Emeralds are factors which are normal but not tolerable into other gemstones.

This means, don’t be surprised when you mine Emeralds and you find all times you don’t get emeralds with no fractures and inclusion free. It is the gem with the most cracks and inclusions; three and two-phase inclusions, fingerprint inclusions, liquid filled inclusions, tube and needle like inclusions, calcite inclusions, angular growth zoning and minerals/crystals inclusions.

In Tanzania Emeralds deposits are available in different places including Manyara: Mbulu Kagera: Karagwe –kyerwa .Morogoro: Mt. Nguru. Rukwa: Sumbawanga-Mpanda.

The international Market receives great majority of Emeralds from Colombia, Zambia, Brazil and Zimbabwe. Other countries which supply emeralds but not in consistent volume to the international market include Tanzania, Russia, Pakistan, Australia, India, Afghanistan and Madagascar.

Geology

Emeralds are formed in either metamorphic rock or sedimentary rock. However, mostly emeralds are formed in regions with metamorphic rock environments, where pegmatite intersects with schists. Emeralds form when beryllium, aluminum, silicon, oxygen and one or more of trace elements like chromium, vanadium and iron that cause its characteristic green color come together in the correct geological environment.

Color Ranges: Emerald has only green color; it is a beryl with green color.

Variety: Emerald belongs to beryl group which has two varieties – Emerald and Aquamarine. Aquamarine is a blue beryl while Emerald is a green beryl.

Emeralds’ Imitations are: Green glass, Synthetic spinel triplet

Synthetic Emeralds: Flux Emeralds and hydrothermal Emeralds

Buyers have alternatives for Emeralds and sometime confuse with: Demantoid garnet, Tourmaline, Diopside, Jadeite, Peridot, Zircon, Tsavorite garnet, Alexandrite.

Gemological properties of Emerald

Gemological Properties of Emerald	Unit of Measure
Gem group	Beryl
Refractive Index (RI)	1.577 to 1.583
Specific gravity	2.72
Hardness (Mohs Scale)	7.5 to 8

Treatment and Grading of Emerald

Fracture filling: filling surface-reaching fractures with colorless oils or resins. Almost 95% of Emeralds are fracture filled because the occurrence of emerald is associated with fractures and inclusions.

                                                             

Emerald Grading	Explanation
A	Vivid Pure Green
B	Deep Green Colour
C	Green Color  with zoning, window and impurities
Traditional Grading
Gem quality	A
Near Gem	B
Industrial/Low quality	C