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Beryl Crystals & Chemistry

Beryl is a beryllium aluminum silicate (Be3Al2Si6O18) formed from some of the most abundant elements on earth with aluminum (8.1%), silicon (27.7%), and oxygen (46.6%). Beryllium is rarer than the other elements present. On average, it is estimated that beryllium comprises only 2.8 grams per ton of crystal rock (Sinkankas 1981).  There are about forty known beryllium minerals, of which beryl is the most common.

Beryl becomes an emerald when there is enough chromium or vanadium, and sometimes iron to color it a specific green color. Without trace amounts of these foreign elements in the crystal, pure beryl is colorless. Other Beryl varieties come in a rainbow of color.  Morganite, heliodor, aquamarine, and even green beryl can all be distinguished from emerald by their color. 


From left to right: Morganite, Aquamarine, and Green Beryl

Beryl comes in a number of varieties aside from emerald, there is also green beryl, heliodor, morganite, bixbite, goshenite, maxixe, and aquamarine. Green beryl does not have coloration that reaches emerald green, like in the example. In this case there is too much yellow in to qualify as emerald. The other varieties are much more straightforward where heliodor is yellow, morganite (named after the banker J. P. Morgan) is pink, bixbite is red, goshenite is colorless, maxixe is dark blue, and aquamarine is a greenish blue to light blue. 

The maxixe color is very rare because the dark blue rapidly fades to colorless in sunlight, unable to even be displayed. The color will come back with irradiation, and will appear when some goshenite and aquamarines with qualifying elements are irradiated.

Emerald Formation

E872 | medium | left | play | “Emerald ID: E872 Weight: 1.19 Carats Origin: Colombia”Emeralds form in two main ways, one is with superheated water with the mixture of necessary elements under the correct pressure. The second way forms with magma instead. The former is how emeralds from Colombia forms, the country that produces around 90% of all gems quality emeralds in the world.

Most gems form through the cooling of mineral rich water or magma. Emeralds have an extra step where specific superheated liquid minerals (aluminum, oxygen, and beryllium) need to come into contact with silica-rich stones like granite. Part of the reason emeralds are so rare is because they need two relatively rare elements in the earth’s crust to form, beryllium and chromium. The numerous requirements makes emerald formation rare, to say nothing of the potential quality that comes out of the deposits.

Crystal Structure

All crystals fall into seven systems. This characterizes the main structure of the gems, and functions as a rule of thumb for how each one behaves.

One of the features of crystals in the hexagonal system like emeralds is that they are pleochroic, meaning the color of the gem changes based on which angle it is viewed from. Emeralds typically display two main colors, making it specifically dichroic. The colors range from green to bluish green, though the exact colors depend on the concentrations of trace elements in the crystal.

Ideally, emeralds will form as a 6 sided prism as a growth habit. Very rarely do gems perfectly form in their ideal crystal habit, and there are usually some anomalies in the growth.

Patricia Emerald as seen in the Museum of Natural History.

Ideal Emerald habit, notice the hexagonal shape.


Cat’s Eye Emerald

Sometimes emeralds will show special features referred to as a phenomena. This is not to be confused with trapiche emeralds since these are a growth characteristic of some emeralds, not a special effect of the light.

Rarely emeralds will have enough needles growing ideally to form a cat’s eye, formally called chatoyancy. The eye is usually fuzzy and ill-defined, and rarely fine-quality. Emeralds that grow as a trapiche are more likely to have this characteristic. Even lumpy, poorly formed ones that are better suited for faceting than a specimen. A pair of fine cat’s eye emeralds were carved from a poorly formed but beautifully colored trapiche emerald.

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