Ruby

Ruby Gemstones

Ruby, a precious gemstone, is renowned for its striking red color, a trait due to traces of chromium. It's a red variety of Corundum mineral, with all other color variants of the same mineral classified as Sapphire. A critical component that sets rubies apart is their hardness, durability, luster, and exceptional rarity, with large transparent rubies being scarcer than diamonds. Despite sharing identical properties with Sapphire apart from color, Ruby has always been classified independently due to its unique allure and historical significance.

The color tone of a Ruby is typically expected to be medium to medium dark-red by most gemological authorities, and any stones lighter than this standard are labeled as pink Sapphire. However, the boundary between Rubies and Sapphires isn't universally agreed upon. The color spectrum for Rubies can span from pinkish to purplish, orangey, and brownish reds, depending on the chromium and iron content, which often varies with the geological location of the ruby's formation. For this reason, terms like "Burmese" or "Thai" are occasionally used to describe Ruby's color, although these do not always correlate with their geographical origin.

Ruby Varieties

• Burma Ruby: Synonymous with Burmese Ruby, referring to rubies sourced from Burma (Myanmar).
• Burmese Ruby: Signifies rubies with exceptional red color, typically associated with those from Burma. It can occasionally be used to describe synthetic rubies as well.
• Pigeon's Blood Ruby: Highly coveted variety of ruby, displaying a blood-red color with a hint of blue.
• Ruby Fuschite: Describes a dark red ruby found in a green Fuschite mica matrix, commonly found in India.
• Ruby Zoisite: A combination of opaque red ruby within green Zoisite, primarily sourced from Tanzania. Ruby Zoisite showcases an attractive contrast and is often used as a minor gemstone, fashioned into cabochons or carved into ornamental figures.
• Star Ruby: Well-known for its display of asterism, often appearing as a six-rayed star pattern on the surface of the stone.

Physical Characteristics of Ruby

Ruby possesses several noteworthy physical properties. On the Mohs scale of mineral hardness, rubies have a rating of 9.0. This places them just below moissanite and diamond in hardness, with diamond being the hardest mineral at 10.0 on the scale. Sapphire, ruby, and pure corundum are classified as α-alumina, which is the most stable form of Al2O3. Each aluminum ion loses 3 electrons in this form, joining a group of six nearby O2− ions in a regular octahedral configuration. Pure corundum, in particular, exhibits a flawless and transparent appearance due to its stable electron configuration.

Crystal Structure of Ruby

In the crystal structure of ruby, the substitution of Al3+ ions (blue) with Cr3+ ions (red) occurs. The density of this substitution, as depicted in the model, is approximately 2%, representing the typical maximum doping encountered. When a chromium atom replaces an aluminum atom, it also loses 3 electrons, becoming a chromium3+ ion to maintain charge balance in the Al2O3 crystal. However, the Cr3+ ions are larger and have electron orbitals oriented differently from aluminum. Consequently, the octahedral arrangement of the O2− ions is distorted, and the energy levels of the Cr3+ ions' orbitals are slightly altered due to their orientation toward the O2− ions. These energy differences correspond to absorption in the electromagnetic spectrum's ultraviolet, violet, and yellow-green regions.

The Role of Chromium in Ruby's Coloration

The presence of chromium in ruby is responsible for its vibrant red color. When approximately 1% of the aluminum ions in ruby are replaced by chromium, the gemstone exhibits absorption in the yellow-green region, resulting in its characteristic red hue. Moreover, when light of specific wavelengths, such as 694 nanometers, is absorbed, it stimulates the emission of fluorescent red light, further intensifying the gem's color and perceived luster. Artificial rubies can be created with chromium concentrations adjusted to be significantly lower than those found in natural gemstones. Consequently, these crystals display a lighter red color, often called pink rubies.

Ruby's Fluorescent Properties and Laser Applications

After absorbing short-wavelength light, ruby enters an excited state within its crystal lattice before fluorescence occurs. During this brief period, if 694-nanometer photons pass through the crystal, they can trigger the emission of additional fluorescent photons, aligning in phase with the initial light. A ruby laser can generate a highly intense, coherent red light by repeatedly passing emitted light through mirrors or other means within the crystal.

Characteristics Distinguishing Natural Rubies

All natural rubies possess imperfections, including color impurities and inclusions of rutile needles known as "silk." Gemologists use these needle inclusions to differentiate natural rubies from synthetic or simulated ones. Typically, rough rubies are subjected to heat treatment before cutting. Presently, most rubies undergo some form of treatment, with heat treatment being the most prevalent—however, untreated rubies of exceptional quality command a significant premium.

Phenomena in Rubies: Asterism and Color Changes

Certain rubies exhibit a striking optical phenomenon known as asterism or "star." These gems are cut into cabochons to showcase this effect properly. Asterisms become visible under a single light source and move across the stone as the light or the stone itself is rotated. This phenomenon occurs due to the reflection of light off the silk, which refers to the structurally oriented rutile needle inclusions. Inclusions, in this case, contribute to the value of the gemstone. Additionally, rubies can display rare occurrences of color changes and chatoyancy, commonly referred to as the "cat's eye" effect.

Ruby vs. Pink Sapphire

Gemstone-quality corundum in various shades of red, including pink, are generally categorized as rubies. However, in the United States, a ruby must meet a minimum color saturation to be classified as such. Otherwise, it will be referred to as a pink sapphire. The distinction between rubies and pink sapphires emerged in the 20th century and remains a topic of debate due to its subjective nature. Trade organizations like the International Colored Gemstone Association (ICGA) have adopted a broader definition of ruby, encompassing its lighter shades, including pink.

Rubies: Treatments and Enhancements

The world of rubies offers several treatments and enhancements to improve their quality and appearance. Heat treatment is a common practice that involves subjecting rubies to high temperatures and controlled cooling to enhance their clarity and color. This process effectively dissolves silk, which refers to rutile inclusions, improving color tone and saturation. However, detecting heat treatment can be challenging as it leaves subtle signs of heat stress visible in residual inclusions.

It's important to note that most rubies have undergone heat treatment unless specified. This practice is widely accepted in the industry, especially when disclosed, and does not significantly diminish the value of ruby gemstones. However, it's essential to exercise caution regarding newer treatments such as diffusion coloring, polymer, and lead glass fillings.

Fracture-filling with lead glass has gained popularity as it transforms previously unsuitable rubies into viable gemstones for jewelry applications. This process involves several steps, including pre-polishing the rough stones, cleaning them with hydrogen fluoride, and subjecting them to two heating processes. The ruby is dipped into oils, covered with lead-containing glass powder, and heated at around 900 °C (1600 °F) for an hour in an oxidizing atmosphere. The powder transforms into a transparent to yellow-colored paste, filling the fractures and dramatically improving the overall transparency of the ruby.

It's worth noting that the treatment can be identified by observing bubbles in cavities and fractures using a 10× loupe. Additionally, when handling rubies set in jewelry, it's important to avoid coating them with substances like boracic acid during repairs, as this can potentially damage the gemstone's surface.

In conclusion, while the heat treatment is widely accepted and does not significantly impact value when disclosed, it's essential to exercise caution regarding newer treatments such as fracture-filling. When considering the purchase of rubies, it's advisable to rely on reputable dealers who can provide proper information and ensure transparency about any treatments or enhancements that have been applied.

Ruby Sources: A Global Overview

Rubies, renowned for their captivating red hue, have been sourced from various regions around the world. While Asia has traditionally dominated ruby production, other continents have also emerged as notable sources. From Myanmar's prized Mogok rubies to Madagascar's treasure trove of gemstones, each origin carries distinct characteristics that influence the value and desirability of these precious gems.

Myanmar, formerly known as Burma, holds a prominent position in the ruby world. Rubies from Myanmar, particularly those from the Mogok region, command high prices due to their exceptional quality. Referred to as "pigeon's blood red," these rubies boast a vivid saturation, dark tone, and a slightly purplish hue. Mogok rubies are renowned for their rich color distribution, often occurring in vibrant patches and swirls. They exhibit remarkable color stability under different lighting conditions, making them highly sought after. Additionally, Mogok is famous for producing the world's finest star rubies, adding to the allure of this legendary deposit.

Another significant ruby mining area in Myanmar is Möng Hsu. In the late 1990s, Möng Hsu emerged as a prolific source of gem-quality rubies. These rubies feature a distinct fluorescent red color and are characterized by their dark core. To enhance their color, Möng Hsu rubies often undergo high-temperature treatments, which have sparked debates within the industry regarding the extent of treatment and its implications for classification.

Sri Lanka, often associated with stunning sapphires, has also produced exceptional rubies. The top-grade Sri Lankan rubies closely resemble their Mogok counterparts, exhibiting similar color qualities. However, Sri Lankan rubies tend to lean towards purple or pink tones. Notably, larger stones in Sri Lanka tend to accumulate more intense color, adding to their magnificence. Sri Lankan rubies exhibit strong fluorescence, and star rubies are also relatively common.

Thailand and Cambodia are renowned for their rubies' high clarity. These rubies, known for their garnet-red color due to a high iron content, lack the silk inclusions that produce asterism or star effect. However, heat treatment is sometimes applied to improve their quality, although it may not be as transformative as in other regions. Rubies from Thailand and Cambodia are considered acceptable options when high-quality material from Myanmar-type sources is not available. However, production from these regions has significantly declined over the years.

Madagascar, famous for its gem wealth, has emerged as a notable ruby source. With deposits located inland from the coastal town of Vatomandry and near the town of Andilamena, Madagascar has showcased its potential in ruby production. The Vatomandry rubies are known for their higher quality, lighter color reminiscent of Myanmar rubies, while the Andilamena rubies are slightly darker and may exhibit less clarity. Both deposits primarily offer heat-treated rubies.

Kenya and Tanzania boast magnificent rubies, albeit in limited quantities of facet-grade material. Similar to Myanmar, rubies from these regions exhibit strong fluorescence. However, star rubies have not been found in these deposits. Furthermore, some regions, such as Songea in Tanzania, produce rubies with a dark, garnet-like color veering towards orange due to their high iron content.

Other notable ruby sources include Mozambique, Afghanistan, Nepal, and Vietnam. Mozambique's Montepuez deposit, discovered in 2009, has become an important source of rubies, offering a wide range of colors and sizes, both treated and untreated. Afghanistan's Jegdalek deposit produces rubies comparable to fine Mogok stones but is limited in terms of facetable material. Nepal is a relatively new source, known for its ruby crystals with varying clarity and color zoning. Vietnam, particularly north of Hanoi and in Luc Yen, has showcased rubies comparable to those from Myanmar, albeit with lower clarity and a tendency towards pink hues.

Understanding the origins of rubies provides valuable insights into their unique characteristics, value, and desirability. From the legendary Mogok rubies of Myanmar to the emerging sources in Madagascar and Mozambique, each origin contributes to the vibrant world of rubies, offering a diverse range of colors, clarities, and traits.

The 4Cs of Ruby Quality: Explained

The same four criteria used for evaluating diamonds are also applied when assessing the quality of rubies. However, there are variations in the standards and importance placed on each criterion regarding rubies. Let's delve into each of the 4Cs to understand what constitutes optimal quality in a ruby:

Color

Describing the color of rubies has historically been a challenge. Ancient manuscripts used terms like "China rose," "saffron," and "pomegranate" to categorize different hues. The most coveted color for rubies is often called "pigeon's blood red," though this intense hue can also be found in rubies from other regions. Today, gemologists assess ruby color based on its hue (including secondary colors), tone (lightness or darkness), and saturation (intensity). The ideal color is a vivid, medium-dark red with slight purplish undertones.

Clarity

Unlike diamonds, rubies rarely possess the high clarity associated with exceptional transparency. Inclusions are common in rubies; even top-quality stones are expected to have visible inclusions under 10x magnification. The preferred clarity grade for rubies is "eye-clean," meaning no inclusions are visible to the naked eye. Inclusions vary based on the ruby's origin and treatment history. Silk inclusions within rubies can create a star effect in cabochon-cut stones, but these typically reduce transparency. The presence of silk and its condition can provide insights into a ruby's treatment.

Carat Weight

Collectors consider rubies over one carat in size rare and highly sought after. Generally, larger rubies command higher prices per carat. However, due to the expensive nature of high-quality ruby rough, calibrated sizes are not commonly cut, as it would result in significant weight loss. Commercial-grade rubies are more likely to adhere to standard calibrated sizes. It's important to note that rubies appear smaller than diamonds of the same carat weight due to their higher specific gravity.

Cut

The term "cut" in the context of rubies refers to various aspects, including the gemstone's faceting style, shape, proportion, and finish. While rubies don't require the precision cuts of diamonds, their beauty is enhanced when they are well-cut. Gem cutters aim to maximize the color display, retain the maximum weight possible, minimize the visibility of inclusions or color zoning, and meet consumer demands for specific cutting styles. Balancing these factors can sometimes lead to compromises, such as sacrificing color or clarity to preserve carat weight.

Understanding the 4Cs allows buyers to make informed decisions when purchasing rubies. Each criterion contributes to a ruby's overall quality and value, and personal preferences play a significant role in selecting the perfect ruby based on its unique combination of characteristics.

Ruby Buying Caveats

It's essential for buyers to be aware of certain considerations when purchasing rubies. Here are a few caveats to keep in mind:

Synthetic Rubies

Lab-created or synthetic rubies have been in production for over a century. These gemstones are chemically and physically identical to natural rubies, making them difficult to distinguish. To ensure you're not unknowingly purchasing a synthetic ruby at the price of a natural one, it's advisable to have your ruby appraised by an independent gemology lab.

Simulated Rubies

Simulated rubies are imitation stones that resemble rubies but are not actually composed of the same materials. They can be made from glass, plastic, or other less expensive gemstones such as garnets or spinels. In fact, many renowned red gemstones that were initially believed to be Rubies turned out to be Spinel upon scientific analysis. Ruby and Spinel often occur together in the same mineral environment and can be found in similar localities.

Colors and Origins

Rubies are found in various locations worldwide, and the trace minerals present in each source can result in subtle color variations. While trade names such as "Burmese," "Thai," or "Ceylon" are often associated with specific ruby colors, they do not necessarily indicate the origin of the ruby accurately. Color alone is not sufficient to determine a ruby's source. It's crucial to rely on other factors such as certification and reputable sellers to ensure the authenticity of a ruby's origin.

Being mindful of these caveats can help buyers make informed decisions and avoid potential pitfalls when purchasing rubies.