The Elements of the Red Emerald
This week, we have compiled selected paragraphs from multiple previous blog posts and articles in order to conduct a review of the basic molecular components which created the Red Emerald!
For colored gemstone synthesis to begin, a minimum of Two Elements must be present. Each serves a separate function: A major Structural element must provide a foundation for the molecule, and a second element must act as a Chromophore -- a metallic ion which absorbs or redirects certain wavelengths to create color from passing light.
Although the same elements present in the Green Emerald also appear in the red beryl from Utah, the addition of a few more cause the Red Emerald variety to form.
1) Red Emerald Structural Element - Beryllium
Diamond famously utilizes carbon atoms to establish a lattice, but Emerald is formed on a molecular foundation of beryllium. "Beryl is a relatively rare mineral because there is very little beryllium in the upper continental crust" (Groat & Laurs - 2009). Emeralds form when beryllium molecules attach to one another using chemical bonds. A mineral must overcome a significant energy barrier for this to occur.
The specific arrangement of molecules relative to the structure of another mineral's atomic lattice is called Oriented Heterogeneous Nucleation. The energy barrier required for crystallization is lowered by taking advantage of a preexisting atomic grid; molecular geometries align and energy is transferred efficiently. The precise location where a mineral connects with another and begins this method of synthesis is called the Nucleation Point.
Hexagonal red beryl molecules often coalesce around a central Bixbyite nucleation until one group begins stacking faster than the others along a preferential vector. This direction of growth may be controlled by external forces -- such as the release of gases and their direction of movement; the crystal may also be impacted by internal causes -- such as lattice orientation in the host mineral. A six-sided tower forms as beryl molecules continue to stack in layers, extending to become a Prism.
2) Red Emerald Chromatic Element(s) - Manganese, et al
Binding together of atoms is a change in the state of valence electrons…In a molecule, the valence electrons of one atom form pairs with the valence electrons of adjacent atoms; these pairs constitute the chemical bonds that hold the atoms together…Only electrons in exceptional states remain to give rise to coloration…One set of unusual electronic states appears in the transition-metal elements, such as iron, chromium and copper and in the rare-earth elements…which have excited states that often fall in the visible spectrum. They are responsible for a wide range of intense colors For example, both ruby and emerald derive their color from trace amounts of chromium (Nassau - 1980).
The GIA defines all colors as having not only hue, but also saturation and tone. To obtain traditional status as an Emerald, a beryl had to exhibit an intensely-saturated color. Before the red varietal was discovered, only the green variety of beryl could satisfy this requirement, and the green alone possessed overly dark tones.
Although their primary hues differ, the same secondary hues (blue and yellow) observed in green Emeralds are also present in the red. When these secondary hues are mixed with a red body color, they appear purple and orange. Both Emerald varieties have intense saturation, dark tones and a range of hues from blue to yellow.
As discussed in later paragraphs, the presence of secondary hues in gemstones demonstrates how more than one coloring ion can contribute to the overall color. William Rohtert identified an additional eleven trace elements in natural red beryl (1995)! The Red Emerald possesses perhaps the most complex color-generation process of any gemstone, but clearly one chromophore cannot be solely responsible for this shade.
In the case of red beryl from the Thomas Range, Nassau and Wood (1968) concluded manganese is the principal coloring agent…Differences in the intensity of color between red beryl and morganite could be due to a higher level of manganese in the former (by two or three orders of magnitude), or to differences in the valence state of this element. However, slight variations among the spectra of these and other pink or reddish manganese-colored compounds prevented Nassau and Wood from fully explaining the observed spectral features of red beryl…[and] specific details still require further investigation (Shigley & Foord - 1984).
If Manganese were the only trace element responsible for the primary hue in Red Emerald, synthetics manufactured with Manganese alone as a colorant would result in similarly-colored gemstones. However, Manganese minerals, such as Pezzottaite and Rhodochrosite, are known to present themselves with a Magenta hue, and red beryl synthetics are immediately identified by this same off-color appearance. As William Rohtert reported to the Gemological Institute of America, "the synthetic displays a more pronounced pleochroism than the natural material."
Pleochroism refers to when a transparent or translucent material displays multiple colors (2 - Dichroic or 3 - Trichroic) when viewed from different angles. A gemstone can exhibit one, two or three colors. Ruby and Red Emerald both possess two matching colors, with a strong Red-Orange/Red-Purple Dichroism. Red Emerald's color does not merely resemble Ruby, but matches that particular crimson EXACTLY.
Chromium produces the Green in Emerald and also the Red in Ruby. This versatility has allowed Chromium to enjoy a recent market preference as coloring ion. As opposites in color theory, Red and Green share a special complimentary relationship, and they are placed together in polar positions.
The presence of Manganese may diminish or inhibit active or primary Chromium participation, but all Chromium (along with the other "non-participating" metallic ions identified by Chemex in 1994) are still placed in symmetrical positions within the molecular order. Even the presence of "inert" Chromium atoms may affect the chromatic behavior of Manganese, because their combined ionic structure produces the EXACT SAME RED Chromium creates alone. Chromium is a prime suspect in shaping this action, since it is the only chromophore ever known to generate this well-known color before.
Is it mere coincidence Chromium and this astonishingly unique Red hue are found together in both occurrences? A logical assessment must consider the role of Chromium in this phenomenon, and a lack of Chromium in synthetic material produced hydrothermally in Russia may explain the lack of correct color.
The action of Manganese is demonstrably controlled, because this metal not only carries a potent Chromatic effect, but the Element is also strongly Structural. "Addition of just a little bit of Manganese completely changes the morphology of a crystal (Rakovan - 2016)." One may rationally expect primary coloration by Manganese to modify the standard appearance of beryl structures. Instead, alterations to standard habits are comparable to the ones observed in Chromium-bearing beryl from Colombia!
Specific modifications to beryl with Chromium (Green) are the same as alterations to beryl with Chromium and Manganese (Red), and both varieties share extraordinarily similar crystallographies. The company of "inactive" chromophores must limit the structural action of Manganese, with any impact on crystal form subordinated or restrained by the presence of others.
Emeralds enjoy a wide color range courtesy of the aforementioned secondary hues blue and yellow. These multiple hues known to exist in a green Emerald illustrate how no single Chromophore is responsible for the entirety of a perceived color. The primary Green of a Colombian Emerald is created by Chromium and/or Vanadium, but the additional influence of Iron and Nickel cause the Yellow and Blue tints, respectively.
The Red Emerald also has Yellow and Blue secondary hues, which mix with Red to appear as the aforementioned Red-Orange/Red-Purple Dichroism. "The color of faceted stones [is] influenced by the mineral’s dichroism…gemstones cut with the table facet oriented parallel to the c-axis typically appear red or purplish red. Conversely, those cut with the table facet oriented perpendicular to the c-axis tend to appear more orangy red (Shigley, Thompson & Keith - 2003)."
The Red of an American Emerald is primarily created by Manganese with Chromium present. Iron is not only responsible for the Yellow undertone in Emerald, but the Yellow/Orange secondary hue in Red Emerald, as well. The Blue in Sapphire is produced by Titanium, which is also suspected of creating the Blue/Purple secondary in Red Emerald.
The chromophores responsible for the colors of our most beloved gems -- Sapphire, Ruby and Emerald -- have combined to create the blush of a Ruby in the body of an Emerald!
The Red Emerald is demonstrably one of the most extraordinary precious gemstone varieties ever fashioned by nature!
Chemex Labs. Red Beryl Sample Analysis: A9417286, Kennecott Exploration Company - June 10, 1994
Rohtert, William R. Internal Memo: Synthetic Red Beryl from Russia, Kennecott Exploration Company - August 14, 1995
Rohtert, William R. Gemological Institute of America Correspondence: Donation of a 1.54 carat Synthetic Red Beryl, Kennecott Exploration Company - March 21, 1996