London, UK – The world of gemstones, often admired for their dazzling exterior, holds an equally captivating, albeit more elusive, universe within. These internal landscapes, known as inclusions, are more than just imperfections; they are microscopic time capsules, offering profound insights into a gem’s geological journey and the ancient environments from which it emerged. While many inclusions are commonplace and familiar to gemmologists, some are so exceptionally rare that encountering them can be a career-defining event. Pat Daly, a distinguished tutor at the Gemmological Association of Great Britain (Gem-A), shares his expertise on these extraordinary internal features, revealing what they signify and why they are considered "once-in-a-lifetime" discoveries.
The Significance of Inclusions in Gemstones
Inclusions are ubiquitous within gemstones. It is exceedingly rare to find a gem entirely devoid of internal characteristics. These can range from pre-existing crystals that were present before the gem’s formation to fluid-filled fissures known as "feathers." The presence and nature of inclusions can dramatically influence a gemstone’s perceived quality and value. In near-white diamonds, for instance, eye-visible inclusions can significantly diminish their market worth. However, in most coloured gemstones, clarity often takes a backseat to the intensity and hue of the colour itself, meaning inclusions may have a less pronounced impact on value, unless they are particularly striking or indicative of origin.
However, inclusions are not merely indicators of a gem’s inherent flaws. In many cases, they are highly desirable. They can serve as irrefutable proof of a gemstone’s natural origin, offering crucial evidence of treatments a stone may have undergone, or, most compellingly, pinpointing its geographical source. Many such inclusions are well-documented and readily identifiable by seasoned gemmologists. Familiar examples include "horsetail" inclusions, often seen in emeralds, or the distinct "tiger stripe" patterns found in amethyst. These recognizable features require little further explanation for those in the know. Yet, there exists a select group of inclusions so uncommon that a gemmologist might spend an entire career without the privilege of examining them firsthand. These are the gems that hold truly exceptional stories.
Unearthing Rarities: A Gemmological Treasure Hunt
Pat Daly’s insights shed light on some of these remarkable, albeit infrequent, inclusions, transforming our understanding of the internal narratives within precious stones.
Ruby Crystals in Diamond: Echoes from the Deep Earth
The presence of bright red crystals within diamonds typically points to chrome-bearing pyrope garnets. Gem-quality diamonds are believed to form under immense pressure and heat, originating from deep within the Earth’s lithosphere and mantle, at depths ranging from approximately 200 to 800 kilometers. Their formation environments are often linked to ultramafic rocks such as peridotites and eclogites.
The occurrence of ruby, a corundum mineral, within a diamond is exceptionally rare and directly linked to eclogite formations. Eclogites are a key rock type where gem diamonds grow, and they can also host other scarce minerals. The discovery of ruby crystals alongside other rare inclusions such as rutile, coesite (a high-pressure form of silica), and blue kyanite within a diamond would be a cause for immense excitement for any gemmologist. Identifying these inclusions not only showcases the diamond’s unique geological history but also signifies a remarkable convergence of rare geological events. Each of these rare finds, if identifiable, would undoubtedly bring profound satisfaction to an enthusiastic gemmologist, offering a tangible connection to the planet’s deep and dynamic past.
Parisite in Emerald: Tracing the Footprint of Rare Earth Elements
"Rare earths" – a group of chemical elements including cerium, europium, and yttrium – are a fascinating subject in gemmology, primarily recognized for the distinctive spectral signatures they impart to certain gemstones, most notably apatite. While rare earth elements are commonly found as trace elements in many minerals, those in which they are essential structural components are considerably less frequent.
Parisite, a carbonate mineral composed primarily of cerium and other rare earth elements, is a prime example. It is found in specific geological settings, notably at Muzo in Colombia. Occasionally, brown crystal inclusions of Parisite are observed within emeralds originating from this renowned locality. The presence of Parisite in an emerald is not only uncommon but also holds significant diagnostic value. Emeralds containing Parisite can exhibit a rare earth spectrum, a characteristic that provides compelling evidence of their natural origin and specific geographical provenance. For a gemmologist, identifying Parisite within an emerald is a remarkable occurrence, offering a direct link to the complex geological processes and mineral assemblages present during the emerald’s formation in the rich deposits of Colombia.
Tourmaline in Kashmir Sapphire: A Geographical Signature
The Kashmir region of India is globally celebrated for producing some of the finest sapphires, renowned for their exceptional velvety blue hue and clarity. While these exquisite stones are highly sought after, more abundant, lower-quality sapphires have also been recovered from the area. Many gemmologists consider themselves fortunate to examine high-quality Kashmir sapphires infrequently, and encountering tourmaline crystals as inclusions within them is an exceptionally rare event.
Transparent green tourmaline crystals, often measuring around 3 millimeters in width, have been documented in the vicinity of sapphire mining sites in Kashmir, approximately a mile away from where the sapphires are extracted. These tourmaline crystals are reportedly brittle and of lesser gem quality themselves. However, their presence within a sapphire is of immense importance. If their identity can be definitively confirmed, tourmaline inclusions serve as powerful indicators, strongly suggesting that the sapphire originates from Kashmir. This makes them incredibly valuable diagnostic tools for gemmologists, as long as they do not detrimentally affect the visual appeal of the sapphire. The confirmation of tourmaline within a sapphire is, therefore, a "once-in-a-lifetime" find that provides crucial geographical authentication.
Animal Fossils in Precious Opal: Glimpses of Ancient Ecosystems
While amber is widely recognized for its ability to preserve ancient insects and other small organisms, providing invaluable scientific specimens, other materials also hold the potential for fossilization. Precious opal, known for its mesmerizing play-of-color, can also act as a remarkable host for preserved remains, including tree roots, twigs, and even more complex organic structures.
In Australia, the unique geological conditions have led to the discovery of opalized fossils, including shells, bones, and, in rare instances, nearly complete skeletons of marine animals. The Lightning Ridge area in New South Wales has yielded the remains of land animals, such as dinosaurs, mammals, and the enigmatic flying reptiles known as pterosaurs, all transformed into opal.
However, the rarest and most delicate of these fossilized treasures are animal fossils composed entirely of opal. A few years ago, a piece of precious opal unearthed from a mine in Indonesia contained a remarkably well-preserved insect. Identified as an immature cicada, most of its body parts were discernible, and even external features like hairs and mouthparts were visible. Estimated to be between 5 and 10 million years old, this specimen was preserved by silica derived from the weathering of volcanic glass. While gemmologists are accustomed to finding insects trapped in amber and copal resin, encountering such a pristine insect within precious opal is an exceptionally rare privilege, offering a unique window into ancient life.
Rare Vertebrate Fossils in Amber: A Window to the Age of Dinosaurs
The preservation of larger animals in amber is generally considered unlikely, as creatures exceeding approximately 20 millimeters in size would typically be able to extricate themselves from sticky tree resin. Despite this, vertebrates are known to be found as fossils in amber, albeit with extreme rarity. Partial, and on very rare occasions, complete lizards have been discovered in amber from regions like the Baltic, Dominica, and Mexico. Reports also include findings of fur, feathers, and snakeskin.
Similarly rare vertebrate remains have been found in Myanmar amber, which is estimated to have formed nearly 100 million years ago during the Cretaceous Period, often referred to as the "Age of Dinosaurs." One of the most extraordinary discoveries in recent years was the reported finding of a small dinosaur skull embedded in Myanmar amber. Measuring approximately 14 millimeters in length, this specimen featured a toothed jaw and was initially believed to be that of an insectivorous dinosaur. Subsequent research on this and another similar specimen has led to the reclassification of these finds, with experts now suggesting they represent lizard-like animals rather than dinosaurs or early birds.
Another significant recent discovery is believed to be a feathered tail, approximately 37 millimeters long, preserved in amber. The structural characteristics of this tail have led to the conclusion that it could not have belonged to a bird. This particular finding represents perhaps the rarest inclusion encountered in gem material to date. The impetus provided by such discoveries is driving intensified searches for similar fossils, potentially leading to further groundbreaking finds. The opportunity to study such an inclusion, which is almost vanishingly rare, would undoubtedly be a career highlight for any gemmologist, offering an unparalleled connection to prehistoric life.
Conclusion: The Enduring Allure of the Inclusions
The study of gemstone inclusions is a cornerstone of gemmology, offering a scientific and historical dimension to the appreciation of these natural wonders. While common inclusions provide valuable diagnostic information, it is the exceptionally rare ones that truly capture the imagination. These "once-in-a-lifetime" inclusions, from ruby crystals in diamond to feathered dinosaur tails in amber, are not merely anomalies but rather extraordinary narratives etched in stone and resin. They speak of immense geological pressures, ancient ecosystems, and the remarkable power of preservation. For gemmologists, the pursuit and identification of these rare internal features represent a profound connection to the Earth’s deep history and the intricate beauty that lies hidden within the heart of every gemstone.
(Main Image Caption): Natural comma-shaped inclusions in emerald, photographed by Pat Daly.
For those new to the fascinating world of gemstones and eager to deepen their knowledge, Gem-A’s mini online course, GemIntro, offers an excellent starting point. Click here to access the course.
