Emerald: learn about its characteristics and the factors that determine its value, and discover the loose emeralds we have for sale
- Carolina Vivas-Serna
- 2 days ago
- 8 min read
The emerald, the famous green beryl, is one of the most coveted precious stones in the world and is a true geological miracle.
Therefore, in this specialized guide I am going to tell you everything you need to know about this gemstone:
Do you want to know more? Keep reading and discover the factors that define it and determine its real value in the international market.
What is an emerald? Rock vs. Mineral
The emerald is a mineral, not a rock (a rock is an aggregate composed of several minerals, such as granite or schist).
The emerald is the green variety of beryl, a cyclosilicate mineral composed mainly of beryllium and aluminium silicate.
Being a mineral, we can state that the emerald is an inorganic solid of natural origin, with an ordered internal structure and a defined chemical composition.
Emerald properties: hardness on the Mohs scale and other characteristics
In order for you to understand the optical behaviour and resistance of emeralds, you must know their physical and chemical characteristics:
Property | Description |
Mineral type | Silicate (subclass Cyclosilicate). Variety of the Beryl species |
Chemical composition | Be3Al2(SiO3)6 (Beryllium and aluminium silicate) |
Hardness (Mohs Scale) | 7.5 to 8 |
Density | 2.67 to 2.78 g/cm³. (Colombian emeralds average 2.70 - 2.71 g/cm³) |
Lustre | Vitreous |
What gives it its colour | Presence of trace elements of Chromium and/or Vanadium substituting aluminium in the crystal structure. Iron may also be present, providing bluish undertones. |
Where is the emerald found and where does it come from?
The main emerald deposits are located in Colombia, Brazil, Zambia, Ethiopia, and Madagascar.
Do you know why emeralds are so valuable? Because their formation requires extreme and rare conditions:
Beryl (mineral) is an element characteristic of continental magmatic rocks (pegmatites).
Whereas chromium and vanadium (the metals responsible for giving the beryl its green colour) are found in the Earth's mantle or in ultrabasic rocks.
This means that the beryl and the metals involved in the formation of the emerald are located in different areas and must meet.
And this meeting occurs, primarily, in zones of contact metamorphism or through hydrothermal fluids.
Why are Colombian emeralds different and more expensive?
Colombian emeralds have a very clean green colour because the pyrite formed first, scavenging the structural iron from the environment.
The origin of Colombian emeralds breaks the global norm because they are not linked to magmatic intrusions, but rather to a hydrothermal-sedimentary process:
During the Cretaceous period, hot brine-laden fluids circulated through tectonic faults in sedimentary black shales.
Then, these fluids leached the chromium and vanadium trapped within the sedimentary rock itself, causing them to combine with the circulating beryllium:
By forming in an iron-free environment, Colombian emeralds exhibit a pure, warm green and an unparalleled natural fluorescence under ultraviolet light.
Without a doubt, this marks a major competitive advantage in the international market.
Why do some emeralds have pyrite?
In Colombia, it is extremely common to find golden pyrite crystals associated with the emerald, either embedded in its matrix or trapped as internal inclusions.
This occurs because both minerals formed in the sedimentary hydrothermal deposits:
When the thermal fluids fractured the black shales, the sulphur and iron reacted with each other to form pyrite (FeS2), leaving the environment “iron-free”.
Then, as mentioned before, the beryl crystallized and combined with the chromium and vanadium, acquiring its green colour.
Therefore, finding pyrite associated with an emerald is not only a visual spectacle but also irrefutable proof of the stone's natural and geographical origin.
What types of emeralds exist?
There are gem-quality transparent emeralds, canutillo emeralds, trapiche emeralds (almost exclusive to Colombia), and morralla emeralds, which are of lower quality.
Unlike precious stones like diamonds or opals, a universal or standard grading system has not yet been created for these gemstones.
Therefore, at Oscar Bautista we classify emeralds based on their transparency and formation pattern.
3.1 Transparent gem-quality emeralds
Transparent emeralds or “crystal emeralds” (as they are known in Colombia), are those that allow light to pass through and have good colour saturation.
In this type of gemstone, natural inclusions do not affect their integrity.
Therefore, they are the stones most commonly used in silver, gold, and platinum jewellery.
3.2 Canutillo emerald
Canutillo emeralds are those that retain their elongated hexagonal prismatic crystal habit intact in the shape of a tube.
We can say that these stones are the Holy Grail for mineral collectors, who value geometric perfection.
In countries like Colombia, this type of emerald is widely used in signature jewellery and high jewellery.
3.3 Trapiche emerald
The trapiche emerald is one of nature's greatest rarities and is almost exclusive to Colombia (it has been found in Brazil and Madagascar, but to a lesser extent).
During the formation of the hexagonal crystal, carbon impurities from the black shale became trapped in the junctions of the six growth sectors.
As a result, a fixed pattern of six symmetrical spokes originating from a central core was formed.
This design resembles the wheel of the Colombian sugar cane mill, known as a “trapiche”, and its name derives from there (take it from me, as I am Colombian).
And well, as you can imagine, the trapiche emerald can reach quite high prices as it is such a rare and special gemstone.
3.4 Morralla emerald
Many Colombian morralla emeralds have pyrite, a mineral that gives them a golden undertone. The presence of pyrite is proof of the natural origin of these stones.
Morralla emeralds are stones with a very high density of inclusions and micro-fractures that limit their transparency.
This means that instead of being transparent or crystalline, they look translucent or opaque.
However, this should not be considered a defect, as the variety of colours and the presence of pyrite give morralla a unique aesthetic personality.
Furthermore, thanks to the cutting process, each stone is transformed into an unrepeatable cabochon emerald, with an accessible price for all types of jewellery.
To see what they look like, take a look at some of the morralla emeralds we have available:
What enhancement treatments are applied to emeralds?
Due to the fractured nature of green beryl, it is estimated that more than 90% of commercial emeralds receive clarity, colour, or stability enhancements.
Therefore, we want you to know what these processes consist of so that you can make informed decisions:
Treatment Name | Process Description | Effect on the Emerald | Impact on its Commercial Value |
Filing with Natural Oils (e.g., Cedar oil) | Introduction of colourless oils of optimum viscosity into fissures open to the surface using pressure and vacuum. | Visually seals fractures by matching the refractive index of beryl, improving apparent clarity. | It is the traditional and historical practice. It maintains the value of the emerald, but requires re-oiling over the years. |
Filling with Artificial Resins (e.g., PermaSafe type polymers) | Injection of stable liquid polymers that enter the fissures of the emerald. | Provides superior structural stability compared to oil. It does not evaporate or wash out easily, protecting the colour and long-term integrity of the stone. | Fully accepted in international trade. Laboratories standardize its value according to the residue level (low, moderate, high), positively valuing the durability it provides to the stone. |
Dyeing (Coloured Oils or Resins) | Introduction of polymeric substances or oils mixed with artificial green pigments. | Artificially alters the real colour of pale or low-quality emeralds. | Reduces the value of the emerald. It must not be sold as natural colour, but as a treatment for colour enhancement. |
Surface Coating | Application of a thin film of green polymer or diamond-like carbon (DLC) on the outer surface of the stone. | Masks external imperfections and superficially and temporarily changes the colour. | Destroys the value of the gemstone. The seller must warn the buyer because the layer deteriorates, scratches, and peels off with daily wear. |
How to identify an emerald and know if it is authentic?
Be careful with home tricks. The best way to know if an emerald is authentic is through the laboratory tests that gemmologists perform.
Sometimes, customers come to our Gem Cutting workshop for us to cut their “emeralds”.
However, upon observing them with a loupe or under a microscope, we break the sad news to them that what they bought are glasses or imitations.
And so that this does not happen to you, we are going to give you two pieces of advice:
The scams in purchasing emeralds are frequent; therefore, analyze the merchant's reputation and look for information regarding their reliability.
If you are going to buy a high-value emerald and need to confirm its authenticity, request a gemmological certificate issued by a recognized entity.
What tests do gemmologists perform to confirm that a stone is indeed an emerald?
In general, these are the tests performed by gemmologists to identify an emerald:
Refractive Index (RI): Using the refractometer, it is verified that the values correspond to beryl (approximate range of 1.577 - 1.583).
Microscopic Inclusion Analysis: Helps to identify the nature and origin of the stone. For example, Colombian emeralds harbour three-phase inclusions.
Polarized Light and Chelsea Filter: Allow for the observation of the optical behaviour of transition elements. Under the Chelsea filter, a chromium-rich emerald shows a pink or reddish reaction.
Advanced Spectroscopy (FTIR and Raman): They detect whether the fissure fillings are oils or polymeric resins, ensuring a transparent diagnosis for the end consumer.
How to care for an emerald?
Due to its hardness on the Mohs scale, the emerald does not scratch easily. However, the presence of inclusions makes it vulnerable to knocks and drops.
There is confusion between two technical concepts related to precious stones: hardness and toughness.
The Mohs scale determines hardness (the resistance of a mineral to being scratched by another).
The emerald, with a score of 7.5 to 8, is a hard mineral; this means that neither dust nor quartz (hardness 7) will scratch it with daily wear.
However, due to its "garden" of inclusions and internal structural tensions, the emerald has low toughness, and this makes it fragile.
In practical terms, a sharp impact against a hard surface can open its fissures or chip the stone.
Therefore, jewellery pieces with emeralds require delicate maintenance.
Tips for cleaning an emerald
These are some of our suggestions if you are going to clean a loose emerald or one set in a piece of jewellery:
Use cold or lukewarm water, liquid soap with a neutral pH, and an ultra-soft toothbrush (such as baby toothbrushes).
Rub with extreme gentleness, rinse, and dry the stone with a soft microfibre cloth.
Completely avoid ultrasonic cleaning, steaming, the use of abrasives, and harsh chemicals such as acetone.
Mechanical vibrations, thermal shock, and contact with certain substances can dislodge the protective oils and resins from the fissures, affecting the integrity and appearance of the emerald.
Buy loose emeralds: discover the gemstones we have available
Want to buy natural emeralds? Discover some of the stones we have available at Oscar Bautista:
