Origin of the Red Emerald
Diamond famously utilizes carbon atoms in its crystal lattice, but Emerald is formed on a molecular foundation of beryllium. In Emeralds, beryllium atoms gather six oxygen each to form a molecule, locking them together in a meta-stable hexagonal ring structure known as the cyclosilicate. This type of formation enjoys a permanence which is aged on a time scale far beyond the human existence.
Cyclosilicates form molecular groups arranged in larger hexagonal plates of beryllium. Like sugar condensing on a wooden stick from a solution to form rock candy, the hexagonal plates can affix to nucleation points, then “stack“ one upon another, forming larger hexagon wafers and even larger prisms. These crystal towers represent the purest form of the mineral beryl. Beryl produces precious and semi-precious stones, because a tremendous amount of beryllium is required for crystallization; beryllium as an element is rare, with a low incidence in the earth's crust.
Six light triangles over six dark triangles graphically represent
molecular hexagonal stacking in beryl.
"A good example of the requirement for [colored gemstone formation to occur in the presence of] a major element and a chromophore is emerald. Beryl is a relatively rare mineral because there is very little beryllium in the upper continental crust" (Groat and Laurs - 2009).
Beryllium is one of the great unknown elements on the planet, as an incredibly strong and lightweight metal. Beryllium is so strong, beryllium tubing is used in satellites which can be struck by comets without a scratch or dent. The lightest bicycle frame in the 2002 Guinness Book of World Records was constructed of beryllium tubing and weighed under five grams.
The American Bicycle Manufacturing company produced a two-pound beryllium bicycle similar to the world's lightest, with the heavy price tag of $25,000.
One method of recovering pure beryllium involves processing non-gem Aquamarine for its molecular content. Thinking of beryllium as refined crushed beryl crystals helps one understand why beryllium is so RARE and EXPENSIVE!
Unsurprisingly, crystallized beryllium, or Beryl, exhibits the same properties of lightness and strength. Emerald is one of the strongest gemstones with a hardness of 8 on the Mohs Scale, but beryl is also lightweight with a low Specific Gravity. In terms of volume, a 0.71 carat Emerald is the same size as a more dense, one carat Diamond. A buyer receives more per-carat when they buy an Emerald!
While collectively under a carat, the small stones in The Purple Ring above represent fine examples of the very rare strong-purple secondary hue.
Some beryl appears under unique conditions we recognize as Emerald. As Diamond has color variants and Sapphire has color variants, Emerald also has a color variant, but the Red Emerald is the rarest precious gemstone in the world. Like Pink Diamonds, Red Emerald crystal sizes are usually small, and the average faceted stone is less than 1/10th of a carat. As with the other pure beryllium gemstones, Red Emeralds are RARE and EXPENSIVE.
The rarest precious gemstone deposits on Earth formed 23 to 18 million years ago, during "large-scale regional crustal extension and thinning…[which caused] rhyolitic magmas [to] rise to the upper levels of the crust, where they are emplaced as shallow, subsurface domes" (Shigley & Foord - 1984). Basically, red beryl deposits are giant "bubbles" of lava which came to rest beneath the surface of the earth.
Cooling lava, or magma, gradually solidifies into igneous rock. The root word IGNITE suggests igneous rocks may provide ideal conditions to birth the red fire owned by our American Emeralds. Instead, as Colorado gem cutter Mark Krivanek correctly assessed, "Nature wasn't kind to those crystals when they were formed…They had to work hard to grow in an incredibly harsh environment."
The green and red beryl are produced as the direct result of volcanic activity. Red Beryl crystallization occurred when temperatures dropped slowly through the range which allowed hexagonal molecules of beryllium to affix upon bixbyite nucleation points drifting in the superheated volcanic melt.
As well as high-temperature, rhyolite magma can be thought of as a high-energy solution. Bixbyite crystals served as electrical resistors through which composite molecules could draw enough energy to bond together. Upon the energy foundation of these bixbyite seed crystals, six-sided molecular beryl plates could coalesce, "stacking" into hexagon wafers and prisms.
As molecular groups increase in size,
hexagonal plates of beryl become visible.
Crystallization may have occurred within two temperature ranges: 1470-870° Celsius and 650-300° C. Rhyolite solidifies between 800-650° C, meaning a high-temperature crystallization would occur with semi-solid conditions, while a low-temperature crystallization would take place under the constraints of a solidified matrix.
Since "high-temperature (>600° C) lithophysal beryls are tabular as opposed to the significantly lower temperature, prismatic beryls, which are hydrothermal in origin" (Foord - 1996), the general consensus has been that Red Beryl "growth occurred at temperatures below magmatic values (~300-650° C)" (Keith, Christiansen & Tingey - 1994).
The apparent flex fracture through the center of this mammoth 39 carat cluster specimen shows the extreme conditions of Red Beryl crystallization.
Perfect crystal formation requires no disturbances over millions of years, yet significant to severe damage can be observed in a majority of crystals. The large-scare crustal extension and thinning hypothesized as present during formation may be a source of injury, but movement of solidified rhyolite to cause cracking across an entire crystal should theoretically leave signs of fracturing in the surrounding undamaged rhyolite.
The Thomas Range and New Mexico deposits produce tabular specimens almost exclusively, which would indicate their formation occurred in a high-temperature environment. While the prismatic habit of the Wah-Wah Mountains suggests a lower range, "Red Beryl forms hexagonal crystals that are hosted by a flow-banded…light gray rock" (Shigley, Thompson & Keith - 2003). Banding suggests high-temperature rhyolite flowing in a less-than-solid state, which may account for movement and crystal damage.
Four thin, vertical, grey flow bands can be counted, with crystal depressions on Line 3 & on Line 4 around the red beryl. Line 1 & 2 are the same band.
"Sharp compositional variations between protogenetic and syngenetic phases…[show] Bixbyite inclusions belonging to two crystallization stages, showing high Fe in the relics, and high Mn in the sharp cubic grains…a temperature of crystallization lower than 950° C for the earlier phase [and] the temperature of final crystallization is about 600° C" (Aurisicchio, et al - 1990).
Crystallization in both temperature ranges may explain why the fractures present in Red Beryl often show signs of healing and a secondary growth period. Two lithologies, or visible magmatic compositions, appear in the red beryl rhyolite flow "as distinct, intermixed portions of strongly flow-laminated rock. The implication is that two magmas were at least partially mixed during eruption and emplacement" (Keith, Christiansen & Tingey - 1994).
As the rhyolite dome settled near the surface, a second infusion of molten material may have entered the "bubble", reheating the mix and improving temperature conditions to create a secondary growth period in either range.
Fluorine encourages crystal formation and was present during Red Beryl growth. Both fluorine and beryllium are available in the surrounding environment, so either or both could have been consumed by the original rhyolite dome as it settled. However, the current consensus contends "the beryllium deposits are near both local and regional faults that probably provided conduits for mineralizing fluids" (Lindsey - 1977). This theory suggests Red Beryl formed in a manner similar to hydrothermal venting, as surface water interacted with cooling magma in the lava dome. However, this explanation does not address the water problem.
"The molecular structure of Emerald consists of rings of silicon with beryllium and aluminum atoms interspersed. The rings are stacked upon one another, forming channels in which a molecule of water can fit. As a result, Emeralds contain up to 2% water" (Ringsrud - 2009).
If a molecule of water is located within a cyclosilicate as the Beryl ring closes, that H2O will be trapped inside for all of our perceptible eternity. Removal would increase stability of the stone, leading gemologists to wonder if it would be possible to take this liquid from inside Emeralds. Imagine what we could learn from a glass filled with a drink from millions of years ago! Despite the dream, no scientist has yet found a way to remove this ancient water.
A gemstone gained the admiration of the ancients any time it was capable of performing a feat no human being could. Such an act is superhuman by definition! While no one has ever been able to remove the water from beryl, nature found a way. The Red Emerald is waterless.
"Every one of the 62 naturally occurring beryls [show] pronounced water absorptions, as do all published natural beryl spectra; analyses usually indicate 0.3 to 3 percent H2O…[but] it is possible to place an upper limit of 0.002 percent on the water present in our [Red Beryl] sample" (Wood & Nassau - 1968).
Perhaps "waterless" is not exactly the right word…but red beryl has one-hundredth to one-thousandth the level of hydro-imprisonment seen in all other beryl! Although any beryl formation is unusual, waterless formation makes the red beryl extraordinarily rare. Most of the world is water, so preventing the entrapment of such a common molecule arouses the speculation as to the manner by which this was achieved.
The prevailing theory of red beryl formation is summarized as follows:
"If the rhyolite flow was partially bathed in surface water during cooling, a water-rich low-density fluid probably permeated shrinkage fractures during beryl formation. Beryllium fluoride complexes reacted with alkali feldspar, water and Fe-Mn oxides along fractures to produce red beryl" (Keith, Christiansen & Tingey - 1994).
This proposed process almost surely would have captured ambient molecules in the surrounding environment, as all other beryl do! As an alternative, if cooling occurred inside the "bubble" without access to the above-ground environment, this hermetically-sealed autonomous atmosphere may account for why the Red Beryl is anhydrous.
Another possible explanation is that any water present was preferentially drawn into surrounding material during the crystallization process. Red Beryl has been found in the rhyolite which completely cooled millions of years ago, alongside "occasional crystals of alkali feldspar, quartz, and minor biotite mica…along with volcanic glass" (Shigley, Thompson & Keith - 2003).
In 1995, William Rohtert studied the composition of this white matrix with Physics International, an offshoot of Lawrence Livermore Lab in San Francisco. After exposing rhyolite to extremely high heat, scientists discovered "the result of plasma streaming formed by the ionization of crystals along grain boundaries culminating in a volcanic-like eruption on the surface of the rock fragment…[indicates] some of the mixed-layer phyllosilicates may have been converted to hydromicas during this process."
Non-Emerald beryls are commonly formed in pegmatites; Colombia produces a water-bearing beryl in a mica schist, while America birthed a waterless beryl in a high-temperature hydro-mica!
There are various opinions on the formation of Red Beryl, but however growth actually occurred, American and Colombian Emeralds both endured compositionally equivalent conditions, resulting in the genesis of visually similar crystals in terms of structures, inclusions and surface modifications. These produce gemstones with comparable optical qualities.
A photo comparison of crystal structures arranged for an article written by consumer advocate & Professional Gemologist (PG) Antoinette Matlins.
There are nuances of Red Beryl crystallography unique to each deposit. In order to properly study the complete portfolio of crystal structures in this mineral variety, I personally visited both Utah mine sites where Red Beryl is found in 2015.
Check out next week's blog to begin a review of those trips with me!
REFERENCES BY DATE OF INFORMATION
Rohtert, William R. Internal Memo: Experimental Technologies, Kennecott Exploration Company - May 31, 1995
Foord, Eugene. Geology, Mineralogy and Paragenesis of the Ruby Violet Red Beryl Deposit, Southern Wah-Wah Mountains, Beaver County, Utah, Kennecott Exploration Company - February 21, 1996