All About Gemstones

There is a moment many people experience the first time they turn a fine Cat's Eye chrysoberyl under a direct beam of light. A sharp, luminous band glides across the surface of the stone like a living thread of silk, appearing to breathe and shift with every slight movement of the hand. It is one of the most arresting sights in the natural gemstone world, and it is entirely the result of physics, not illusion. These visual phenomena, known collectively as optical effects in gemstones, are among the most misunderstood and underappreciated qualities a natural stone can possess. Special optical effects in gemstones refer to light interactions caused by structural features within the stone itself: needle-like inclusions, microscopic growth layers, structural symmetry, or intergrowth patterns. They include asterism (the star effect), chatoyancy (the cat's eye effect), adularescence, labradorescence, iridescence, and colour change. Each effect is governed by different internal architecture and occurs in different gemstone families. Understanding them helps buyers choose with intention, and helps astrology enthusiasts recognise why certain stones have held sacred significance across Vedic tradition for centuries. This article covers every major optical effect found in natural gemstones sold in India, the gemological science behind each, the Vedic astrological context where it applies, and what to look for when evaluating a stone. By the end, you will know exactly what separates a fine star ruby from an ordinary one, why a Cat's Eye (Lehsunia) displays its beam only in certain lighting, and which optical effects carry astrological significance according to classical Vedic texts. What Are Optical Effects in Gemstones and Why Do They Occur Optical effects in gemstones are visual phenomena produced when light interacts with internal structural features rather than with the stone's base chemistry or colour alone. These effects are not surface treatments or coatings. They arise from the natural architecture of the crystal itself, built up over millions of years in the earth. The three primary structural causes are as follows. First, the presence of oriented inclusions, typically fine needle-like crystals called rutile, which align in parallel rows along the crystal's growth axes. Second, microscopic layering or twinning within the crystal structure, which creates interference patterns as light bounces between layers. Third, the arrangement of internal growth zones or intergrowths between two different mineral phases within the same stone. Why Inclusions Create Light Effects Most gemstone buyers are taught to think of inclusions as flaws. In optically active stones, the opposite is true. Without a dense population of fine, well-oriented needles inside a star ruby (Manik) or star sapphire (Neelam), no asterism would exist. The rutile needles in corundum, for example, grow along three crystallographic directions, each set at 60 degrees to the others. When light enters the curved, dome-shaped surface of a cabochon-cut stone and strikes these needles, it scatters into three intersecting bands of light, producing the six-rayed star effect. In Cat's Eye stones, the needles or hollow tubes align along a single axis. The curved cabochon surface focuses reflected light into one sharp band rather than three, producing the chatoyancy effect. The same underlying principle, oriented reflectors interacting with a curved surface, governs both phenomena. The Role of Crystal Structure and Cut The cut of a stone is as important as its inclusions in producing a visible optical effect. A flat-cut ruby with dense rutile inclusions will show a hazy, silky lustre but no star. The same material, cut as a high-domed cabochon with the dome centred precisely over the crystal's c-axis, will display a clean, well-centred star. This is why experienced lapidaries who work with star material in Jaipur study the rough stone under strong directional light before making a single cut. The optical centre of the rough determines the final placement of the dome. Asterism in Gemstones: The Science and Significance of the Star Effect Asterism is the optical phenomenon in which a gemstone displays a star-shaped pattern of reflected light, typically with four, six, or twelve rays, when illuminated by a single light source and viewed through a curved cabochon surface. It is one of the most prized optical effects in the natural gemstone world, and it carries significant astrological weight in Vedic tradition. The word comes from the Greek aster, meaning star. The effect is caused by oriented needle-like inclusions of rutile, ilmenite, or hollow growth tubes aligned along multiple crystallographic axes within the crystal. When the cabochon's dome is correctly oriented and a point light source is used, the reflected light from each set of parallel needles converges to produce one ray, and the intersection of all rays creates the star. Six-Rayed Stars: Ruby and Sapphire The most famous asterism stones in India are star ruby and star sapphire, both members of the corundum family with a Mohs hardness of 9. Corundum has a trigonal crystal structure with three pairs of rutile needle orientations, each pair producing one ray of the star. The result, when the cabochon is well-cut, is a sharp six-rayed star. Fine star rubies are sourced from Burma and Mozambique; fine star sapphires come primarily from Sri Lanka, where the trade in star material from the Ratnapura district has been documented for over a thousand years. According to Vedic astrology, both ruby (Manik) and blue sapphire (Neelam) are among the most powerful planetary gemstones in the Navagraha system. Manik governs Surya (the Sun), the graha associated with authority, vitality, and social standing. Neelam governs Shani (Saturn), whose influence over karma, discipline, and transformation is described in detail in the Brihat Parashara Hora Shastra, one of the foundational texts of Jyotish. The astrological potency of these stones is traditionally considered independent of the star effect. However, star varieties are often regarded by astrologers as rare natural formations that demonstrate the purity and internal organisation of the crystal, qualities aligned with clear planetary energy. At Myra Gems, our gemologists regularly encounter customers who are drawn to star rubies and star sapphires precisely because of the visual drama they offer. The most common question we receive about these stones is whether the star should be sharp or diffuse. The answer depends on the material: a fine star should have rays that are straight, well-defined, and centred on the dome, visible under a single incandescent bulb or torch light. Four-Rayed and Twelve-Rayed Stars Not all asterism stones produce six rays. Garnets and some rare diopside specimens display four-rayed stars, the result of inclusion orientations that align along only two crystallographic axes. Rose quartz, sourced from Brazil and Madagascar, famously produces a six-rayed star but in a diffuse, milky form caused by microscopic inclusions of aligned fibrous minerals rather than rutile needles. Twelve-rayed stars occur in some corundum specimens where two generations of rutile growth have occurred at different stages in the crystal's history, producing two overlapping six-rayed star patterns. Quick Answer A six-rayed star in corundum (ruby or sapphire) is produced by three sets of oriented rutile needles aligned at 60 degrees to each other within the crystal. Cause Oriented rutile or ilmenite needle inclusions Best cut High-domed cabochon, c-axis centred under dome Primary gemstones Star ruby, star sapphire, star garnet, rose quartz Ray count 4, 6, or 12 depending on crystal structure Light source needed Single point light (torch, direct sunlight, incandescent bulb) Astrological gemstones Star Manik (Surya), Star Neelam (Shani)   Explore Natural Gemstone Rings at Myra Gems At Myra Gems, every natural gemstone ring in our collection is selected for quality, optical character, and authenticity. Our cabochon-cut stones are examined for centring and ray sharpness before they enter the collection. Explore our full collection of natural gemstone rings Chatoyancy: What Creates the Cat's Eye Effect in Gemstones Chatoyancy is the optical effect that produces a single luminous band of light across the surface of a cabochon-cut gemstone, resembling the vertical slit pupil of a cat's eye. It is caused by the reflection of light from a dense concentration of parallel needle-like inclusions or hollow tubes aligned along a single crystallographic direction within the stone. The French word chatoyant means "shimmering like a cat's eye," and the effect has been observed and prized in India for centuries. When gemologists use the term "Cat's Eye" without qualification, they are referring specifically to chrysoberyl cat's eye, the gold standard of chatoyant stones. All other chatoyant gems must be identified by their mineral name: Cat's Eye aquamarine, Cat's Eye tourmaline, Cat's Eye scapolite. Chrysoberyl Cat's Eye and the Vedic Lehsunia The gemological benchmark for chatoyancy is chrysoberyl, a beryllium aluminium oxide with a Mohs hardness of 8.5 and a refractive index range of 1.746 to 1.763. Fine chrysoberyl cat's eye from Sri Lanka and India's own Odisha mines displays what the trade calls the "milk and honey" effect: when a penlight is held to one side of the stone, the illuminated half appears honey-gold while the shaded half shows a milky, almost creamy tone. This bilateral colour split is considered the hallmark of a top-quality cat's eye. According to Vedic astrology, Cat's Eye (Lehsunia) is the gemstone of Ketu, the south lunar node. Ketu is a shadow graha, described in classical Jyotish texts as governing spiritual liberation, sudden events, and the severing of attachments. Astrologers traditionally recommend Lehsunia for individuals in Ketu's mahadasha or antardasha periods, and the Ratnapariksha, an early Sanskrit text on gemstone evaluation, specifically describes the Cat's Eye as a stone whose sharp, centred beam is a sign of purity and auspicious influence. A natural, untreated Cat's Eye chrysoberyl can be identified by the sharpness and mobility of its band: the beam should move cleanly across the dome as the stone is rotated, and it should split into two bands when two light sources are directed at the stone simultaneously. This "opening and closing" behaviour, called the opening effect in the trade, is a reliable indicator of genuine chatoyancy in fine material. Other Chatoyant Gemstones in India The most commonly encountered chatoyant stones in the Indian market beyond chrysoberyl include Cat's Eye tourmaline, Cat's Eye aquamarine, Cat's Eye opal, and silky Tiger's Eye quartz. Tourmaline cat's eye is notable because tourmaline grows with long parallel hollow tubes along its c-axis, producing strong chatoyancy without rutile needle inclusions. Tiger's Eye, found primarily in South Africa and available in the Indian market through Jaipur's gem trade, owes its silky shimmer to the pseudomorphic replacement of crocidolite asbestos fibres by quartz, which preserves the fibrous parallel structure in an oxidised golden-brown form. Gemologists recommend evaluating all chatoyant stones under a single narrow light source. Diffused room lighting will suppress or obscure the band entirely, making a genuine cat's eye appear to be an ordinary cabochon. This is one of the most important practical points when buying Cat's Eye stones in India's informal gem markets. Adularescence and Labradorescence: The Glow Within Adularescence and labradorescence are two distinct optical phenomena caused by the scattering and interference of light within layered internal structures, producing a glowing, billowing light effect that seems to originate from inside the stone rather than from its surface. These are the defining optical characters of moonstone and labradorite respectively. Both effects are caused by a structural phenomenon called exsolution lamellae: alternating thin layers of two different feldspar compositions that form as the crystal cools slowly over geological time. The thickness of these layers determines which wavelengths of light are scattered, and therefore which colours appear. Adularescence in Moonstone Moonstone is a variety of orthoclase feldspar known for its blue-white adularescent glow, which moves across the stone as it is tilted. The finest moonstones, historically sourced from Sri Lanka's Meetiyagoda mines, show a strong blue adularescence over a colourless to pale body colour. The specific gravity of moonstone falls between 2.56 and 2.59, and its Mohs hardness of 6 to 6.5 makes it softer than most other gemstones used in jewellery, requiring protective settings. The most important factor when buying moonstone is the quality and direction of the adularescent glow. It should appear to float above the body of the stone like a full moon reflected on still water, rather than sitting flat on the surface. This optical depth is produced by the thickness and uniformity of the internal lamellae. Thin, uniform layers produce the classic blue glow; thicker layers scatter longer wavelengths and produce a white or silver shimmer instead. Labradorescence in Labradorite Labradorite, a plagioclase feldspar primarily sourced from Canada, Finland, and Madagascar, displays an effect called labradorescence: a spectral play of colours, most commonly vivid blue, green, gold, and orange, that appears only at specific angles of observation. Unlike adularescence, which produces a single floating glow, labradorescence shows different colours depending on the viewing angle, because different thicknesses of the alternating feldspar lamellae reflect different wavelengths. The most prized form of labradorite is Spectrolite, a trade name for material from Finland that displays the full visible spectrum within a single stone. Standard labradorite from Madagascar and Canada typically shows blue and green labradorescence. The phenomenon is entirely structural and natural, requiring no treatment or enhancement. Colour Change in Gemstones: The Alexandrite Effect Colour change is arguably the most dramatic of all optical effects in gemstones. A true colour change gemstone appears to be one colour in daylight or fluorescent light and a completely different colour under incandescent or candlelight. The most celebrated example is alexandrite, a rare variety of chrysoberyl that appears green to blue-green in daylight and red to purplish-red under incandescent light. The colour change in alexandrite is caused by an unusual interaction between the stone's chromium content and the human eye's colour perception system. Chromium absorbs strongly in the yellow-green portion of the visible spectrum, leaving transmitted light composed primarily of green and red wavelengths. Daylight, which is rich in blue-green wavelengths, tips the balance toward green perception. Incandescent light, which is richer in red wavelengths, tips the balance toward red. The result is a stone that appears to transform completely depending on the light source. Alexandrite: Rarity and Value in the Indian Market Fine alexandrite is among the rarest gemstones in commercial trade. The original source, the Ural Mountains of Russia, is largely exhausted. Today, the principal sources are Sri Lanka, Brazil, and East Africa, particularly Tanzania and Zimbabwe. Alexandrite from Sri Lanka tends to show a softer colour change, green to brownish-red. Brazilian and East African material can show stronger red tones in incandescent light. Regardless of origin, a strong, clean colour change with saturated hues in both lighting conditions is the primary quality factor. The traditional guidance in the Indian gem trade is that alexandrite should show a colour change that is immediately visible to the naked eye under both light sources, without requiring tilting or manipulation. A faint or murky colour change indicates lower-grade material or a simulant. According to Vedic astrology, alexandrite is not assigned to a specific graha in classical texts, as it was not historically available in ancient India. Contemporary Jyotish practitioners sometimes associate it with Budh (Mercury) on account of its dual nature and green daytime colour, but this is a modern interpretation rather than a classical prescription. Need Guidance on Which Gemstone Is Right for You? Choosing the right natural gemstone involves understanding both its optical character and its Vedic astrological significance. Our gemstone guidance page brings together expert advice from Myra Gems' in-house team to help you navigate this decision. Visit our Gemstone Guidance page Iridescence and Orient: Surface and Sub-Surface Light Play Iridescence in gemstones refers to the display of spectral colours across the surface of a stone, produced by the interference of light waves reflected from thin films or layered structures near or at the surface. It is distinct from labradorescence, which occurs within the body of the stone, and from adularescence, which produces a diffuse glow rather than spectral colour bands. The most significant iridescent gemstone in the Indian astrological tradition is Pearl (Moti), whose orient, the soft, multi-coloured iridescence visible across the surface of fine nacre, is produced by the interference of light within the microscopic aragonite platelet layers of the pearl's nacre coating. Pearl governs Chandra (the Moon) in Vedic astrology, and fine natural pearls with strong orient have been described as auspicious in classical Jyotish literature going back to the Brihat Parashara Hora Shastra. At Myra Gems, we source natural freshwater and saltwater pearls selected for strong orient and clean nacre, two qualities that are inseparable from the stone's astrological character. Orient in Pearl vs Surface Lustre It is worth distinguishing between the lustre and the orient of a pearl, as these are frequently confused. Lustre is the mirror-like reflective quality of the surface, the sharpness of reflected images seen on a pearl's outer layer. Orient is the soft, rainbow-like iridescence that appears to float slightly below the surface, caused by interference of light within the nacre layers themselves. A fine pearl can have excellent lustre but weak orient, or moderate lustre with strong orient. For astrological purposes, orient is traditionally considered more significant, as it reflects the depth and quality of the nacre growth rather than simply its surface polish. Iridescence in Opal Opal produces its play of colour through a completely different mechanism from pearl. Precious opal contains a three-dimensional lattice of uniform silica spheres arranged in a regular grid. When these spheres are sufficiently uniform in size and spacing, they act as a diffraction grating, splitting white light into its spectral components and producing the vivid flashes of colour known as play of colour. The specific colours displayed depend on the size of the silica spheres: smaller spheres produce violet and blue; larger spheres produce red and orange. Play of colour opal is sourced primarily from Australia, Ethiopia, and Mexico. Opal is not assigned a primary graha in classical Vedic texts, but it is associated with Venus (Shukra) by many contemporary astrologers on account of its association with beauty, creativity, and emotional sensitivity. The natural opal rings in Myra Gems' collection include both Australian and Ethiopian material selected for vivid, full-spectrum play of colour. How to Evaluate Special Optical Effects When Buying Gemstones in India Evaluating optical effects in natural gemstones requires the right lighting conditions, the right knowledge of what a genuine effect looks like in each stone type, and an understanding of how these effects are commonly imitated or misrepresented in the market. This section covers the practical steps that any buyer in India should follow before purchasing a star stone, cat's eye, colour change stone, or adularescent gem. The most important factor when buying any optically active gemstone is to evaluate it under the correct light source. Each effect is produced by a specific type of light interaction, and viewing a chatoyant or asterism stone under diffuse fluorescent room lighting will suppress the effect almost entirely, making it difficult to evaluate quality accurately. Correct Light Sources for Each Effect The following guide covers the lighting conditions required to assess each optical effect accurately. Asterism (star effect): requires a single point light source, ideally a penlight or a narrow-beam torch, held directly above the stone. A curved cabochon must be used. The star is invisible under diffuse or ambient lighting. Chatoyancy (cat's eye effect): requires a single narrow light source directed across the dome of the cabochon. The band should be sharp and mobile. Two light sources should cause the band to open. Adularescence (moonstone glow): visible under most lighting conditions but most dramatic under a single backlight or diffuse overhead source. The glow should appear to float inside the stone, not sit on the surface. Labradorescence: requires changing the angle of the stone relative to a fixed light source. The colour appears and disappears as the viewing angle changes. Colour change: requires two separate light sources, one daylight or cool white fluorescent, one warm incandescent or candlelight. The stone must be evaluated under both and the colour difference noted. Play of colour in opal: visible under most lighting but most vivid under direct sunlight or a focused halogen source. The colour should appear in broad, rolling flashes, not as a single static patch. Quick Answer Each optical effect requires a specific light source to be properly evaluated; using diffuse room lighting suppresses most effects and makes quality assessment unreliable. Asterism Penlight or narrow torch, directly above the dome Chatoyancy Single narrow light source, directed across the dome Adularescence Diffuse or backlit source, note depth of glow Labradorescence Fixed light, change viewing angle Colour change Evaluate under both daylight and incandescent light Play of colour (opal) Direct sunlight or focused halogen Detecting Imitations and Enhancements At Myra Gems, our gemologists regularly encounter customers who have previously purchased star rubies or cat's eye stones from informal markets and are uncertain whether the effect is genuine. The most common imitations to be aware of are the following. Composite or doublet star stones: a thin layer of natural corundum with rutile inclusions is cemented onto a base of glass or synthetic material. The star is real but the stone is not entirely natural. The seam at the girdle is usually visible under magnification. Glass cat's eye: glass can be manufactured with parallel fibres to simulate chatoyancy. The band in glass tends to be broader and less sharp than in genuine chrysoberyl, and the "milk and honey" bilateral effect is absent. Synthetic alexandrite: laboratory-grown alexandrite shows a strong colour change that often surpasses fine natural material. Identifying natural versus synthetic alexandrite requires gemological testing, as the two are chemically identical. The presence of natural inclusions, fingerprints, and growth features is the primary indicator of a natural stone. Surface coating and foiling in opal doublets: thin slices of natural opal are cemented to a black backing material to intensify the play of colour. Viewed from the side, the layered construction is visible. Genuine precious opal shows play of colour through its full depth. What to Know Before Buying an Optically Active Gemstone: Advice from Myra Gems' Gemologists Over more than 30 years of sourcing natural stones from Jaipur, Sri Lanka, Burma, and East Africa, the team at Myra Gems has developed a set of practical principles for evaluating and buying optically active gemstones. The following tips reflect observations made across thousands of transactions with customers across India. The first principle is that optical effects are always best evaluated in person, under proper lighting. Photographs and videos of star stones and cat's eyes are inherently misleading because they are taken under controlled light optimised to show the effect at its strongest. A stone that looks dramatic in a photograph may show a weak or off-centre effect in hand. The second principle is that the centring of the optical effect is as important as its strength. A star ruby whose star is centred on the dome when the stone is held face-up is worth significantly more than an equally bright star that sits off-centre. The same applies to the cat's eye band: a centred, sharp band that runs exactly from one edge of the cabochon to the other is the standard of quality. An off-centre or curved band suggests the stone was cut without adequate attention to the optical axis of the rough. The third principle is that the body colour of an asterism stone matters independently of the star. A fine six-rayed star in a pale, washed-out ruby is less valuable than the same star quality in a deeply saturated, natural, unheated stone from Burma. The star should complement the colour, not compensate for its absence. The fourth principle concerns durability. Moonstone, with a Mohs hardness of 6 to 6.5 and a tendency toward cleavage, requires protective settings such as bezel mounts rather than prong settings. Opal, at 5.5 to 6.5 on the Mohs scale, is similarly fragile and must be protected from impact, low humidity, and rapid temperature changes. Cat's Eye chrysoberyl, at 8.5, and corundum, at 9, are among the hardest gemstones available and are suitable for everyday wear in rings. The fifth principle applies specifically to Vedic astrological use. According to Vedic astrology, the optical effect in a gemstone is a consequence of its internal structure, not an astrological enhancement in itself. A star ruby is still a ruby, governed by Surya, and its planetary influence is determined by its quality as a corundum, not by the presence or absence of asterism. Astrologers generally recommend selecting the finest quality stone available within one's budget, prioritising colour, clarity, and origin over the presence of a rare optical phenomenon, unless the individual has a specific astrological reason to seek star material. The sixth principle is about natural versus treated material. Many star corundum stones on the Indian market have been subjected to heat treatment to improve or induce the star effect by precipitating dissolved rutile from the crystal lattice. While heat treatment is standard practice for colour enhancement in faceted corundum, heat treatment specifically to induce or improve asterism affects the astrological classification of the stone in the view of many traditional Jyotish practitioners. The traditional guidance is that a naturally formed star, produced by inclusions present in the rough stone as it came from the earth, is preferred for astrological purposes. See our guide to heated versus unheated gemstones for a full explanation of how treatment affects a stone's classification. Trusted by Over 30,000 Customers Since 2008 Myra Gems has been India's destination for natural, authenticated gemstone jewellery for over 30 years. Our gemology team selects every stone with the same rigour we apply to astrological recommendations: origin, optical character, and natural condition. Explore the full Myra Gems collection Frequently Asked Questions About Optical Effects in Gemstones Q: What is the difference between asterism and chatoyancy in gemstones? A: Asterism produces a star pattern of two or more intersecting rays of light across a cabochon surface, while chatoyancy produces a single band of light resembling a cat's eye. Both are caused by oriented needle-like inclusions within the crystal, but asterism requires inclusions aligned along multiple crystallographic axes (typically three, producing six rays), while chatoyancy requires inclusions aligned along only one axis. The classic asterism stones are star ruby and star sapphire; the classic chatoyancy stone is chrysoberyl Cat's Eye, known in Vedic astrology as Lehsunia. Q: What gemstone shows the cat's eye effect in Vedic astrology, and which planet does it represent? A: In Vedic astrology, the Cat's Eye gemstone used for astrological purposes is chrysoberyl Cat's Eye, known as Lehsunia. It is the gemstone of Ketu, the south lunar node. Ketu governs spiritual liberation, sudden reversals, and the karmic influence of past lives according to classical Jyotish texts. Astrologers traditionally recommend Lehsunia for individuals running Ketu's mahadasha, and the stone is worn on the middle finger of the right hand. Only chrysoberyl qualifies as Lehsunia for astrological purposes; Cat's Eye tourmaline, quartz, or other stones are not considered substitutes in classical Vedic practice. Q: Does a star ruby or star sapphire have the same astrological effect as a faceted ruby or sapphire? A: According to Vedic astrology, both a star ruby and a faceted ruby are governed by Surya (the Sun) and carry the same planetary association. The star effect is a consequence of the stone's internal structure and does not change its astrological classification. However, some contemporary Jyotish practitioners consider star material to represent a particularly concentrated expression of the stone's planetary energy, as the internally organised structure reflects the stone's natural purity. The primary astrological quality factor remains the stone's colour, origin, and natural, untreated condition, not the presence of asterism. Q: How can I tell if a cat's eye effect is genuine or produced by glass? A: A genuine Cat's Eye chrysoberyl shows a sharp, narrow, mobile band of light that moves cleanly across the dome as the stone is rotated. When two light sources are directed at the stone, the band should split into two separate rays, opening and closing like a cat's pupil. This opening effect is absent in glass imitations. Glass cat's eye tends to show a broader, flatter band without the characteristic bilateral "milk and honey" colour split seen in fine chrysoberyl. The refractive index and specific gravity of chrysoberyl are also distinct from glass and can be verified by a qualified gemologist. When buying Cat's Eye stones in India's informal markets, always request evaluation under a proper penlight. Q: What causes the colour change in alexandrite? A: Alexandrite changes colour because its chromium content absorbs selectively in the yellow-green portion of the visible spectrum, leaving transmitted light composed of both green and red wavelengths. In daylight or cool white light, the eye's colour receptors respond more strongly to the green component, making the stone appear green. Under incandescent or warm candlelight, the red component dominates, and the stone appears red to purplish-red. This is not a surface effect and cannot be induced by treatment; it is an inherent optical property of chromium-bearing chrysoberyl. The strength of the colour change in alexandrite depends on the chromium concentration and the specific absorption profile of each individual stone. Q: What is adularescence and which gemstone is known for it? A: Adularescence is the soft, billowing glow of light that appears to float inside a moonstone as it is moved. It is caused by the scattering of light within alternating thin layers of two different feldspar minerals, orthoclase and albite, that form as the crystal cools. The finest moonstones, from Sri Lanka's Meetiyagoda region, show a vivid blue adularescence over a near-colourless body. Adularescence is entirely natural and structural; it cannot be induced by treatment. The effect is distinct from surface lustre: adularescence appears to come from within the stone, giving moonstone its characteristic ethereal quality. Q: Is play of colour in opal the same as iridescence? A: Play of colour in precious opal and iridescence are related but technically distinct phenomena. Play of colour is caused by diffraction of light through a regular three-dimensional lattice of uniform silica spheres inside the opal, splitting white light into its spectral components. Iridescence, in a broader sense, is caused by thin-film interference or diffraction at or near a surface. The play of colour in opal appears as vivid, rolling flashes of spectral colour that change with viewing angle; it is a highly organised optical effect specific to precious opal. Iridescence in pearl, known as orient, is caused by interference within the nacre's aragonite platelet layers and produces a softer, more diffuse spectral shimmer. Q: Why does moonstone show its glow only from certain angles? A: Moonstone's adularescent glow is directional because the scattering of light that produces it occurs only when light enters the stone at angles that allow it to interact with the internal lamellae, the alternating layers of feldspar minerals within the crystal. When the stone is oriented so that light travels perpendicular to these layers, scattering is maximised and the glow is strongest. At other angles, the light passes through the lamellae without sufficient interaction and the glow diminishes. This is why the cabochon cut is essential for moonstone: the dome must be oriented to keep the most responsive direction of the crystal facing upward toward the light source. At Myra Gems, all moonstone cabochons are orientated by our lapidary team to optimise the adularescent display before the stone is set. Q: Does Myra Gems carry star rubies, star sapphires, and Cat's Eye stones? A: Myra Gems carries natural ruby rings and sapphire rings selected for quality and natural condition. Customers interested in star material or Cat's Eye chrysoberyl for astrological purposes are welcome to contact our team directly through the Gemstone Guidance page or book a video consultation to discuss specific requirements. Our gemologists can advise on the availability of star material and Cat's Eye stones suitable for Vedic astrological use, including guidance on quality factors relevant to the governing graha. Q: Can optical effects like asterism or chatoyancy be created artificially? A: Asterism can be induced in corundum through heat treatment. When rutile inclusions in ruby or sapphire rough are dissolved into the crystal by high-temperature heating and the stone is then cooled slowly under controlled conditions, fine rutile needles re-precipitate in an oriented arrangement, producing or strengthening the star effect. This process is well known in the gem trade and affects the astrological classification of the stone in the view of many traditional Jyotish practitioners, who prefer naturally formed stars. Chatoyancy in chrysoberyl cannot be artificially induced; the parallel hollow tubes that produce the cat's eye effect in chrysoberyl form only during natural crystal growth. Glass cat's eye imitations can be manufactured by embedding parallel fibres in glass, but these are identifiable by gemological testing. Understanding Optical Effects in Gemstones: Key Takeaways Natural optical effects in gemstones, from the six-rayed stars of corundum to the billowing glow of moonstone and the luminous beam of a Cat's Eye chrysoberyl, are among the most compelling expressions of the earth's geological processes. Each effect is unique to the internal architecture of the stone that produces it, and each requires specific lighting conditions, a correct cut, and a trained eye to evaluate properly. For those interested in Vedic astrology, the relationship between a gemstone's optical character and its planetary association is one of the most nuanced areas of classical Jyotish knowledge. The information in this article is for educational purposes; consult a qualified Vedic astrologer before selecting and wearing any gemstone. The governing graha, the quality of the material, and the individual's birth chart together determine which stone is appropriate, and optical effects, while visually extraordinary, are one element of that larger picture. Myra Gems has been guiding customers across India through these decisions for over 30 years. Whether you are drawn to the drama of a star ruby, the calm precision of a Cat's Eye, or the ethereal shimmer of a moonstone, the starting point is always a natural, authentic stone evaluated with care. Explore the natural gemstone ring collection at Myra Gems to find stones selected for both optical character and gemological integrity.