Picture 1: Rough Sapphire
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
Picture 2: Cut and Polished Sapphire into a ring
Geology
The earth’s three most abundant elements are Aluminum, Oxygen and Silicon.Crundum which is a group of sapphire is only composed of Aluminum and Oxygen, this means it requires growth environment that is free of silicon. This makes natural Sapphire (corundum) relatively rare.
In its purest state corundum is colourless.When mixed with trace elements of iron and titanium, the corundum becomes blue sapphire. The more the iron, the more sapphire becomes darker blue.
Sapphire can form into basalt, non-basalt, pegmatite and rarely into igneous rocks. Those formed into basalt rocks, becomes darker than those from other rocks. The most valuable color of Sapphire is a cornflower blue color, known as Kashmir Sapphire or Cornflower Blue Sapphire. Another extremely valuable Sapphire form is the orange-pink called Padparadschah, and an exotic type of sapphire, known as Color Changing Sapphire, displays a different color depending on its lighting. In natural light, Color Changing Sapphire is blue, but in artificial light, it is violet.
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 Colour |
| C | Deep colour with window and impurities |
| Traditional Grading | |
| Gem quality | A |
| Near Gem | B |
| Industrial/Low quality | C |