A Glossary of
Colored Gemstones
A reference guide to the language of fine colored gemstones — drawn from gemological practice, trade convention, and seven generations of family expertise. Each term is defined plainly, so that collectors, inheritors, and the curious can read a lab report, follow a market conversation, or evaluate a piece with greater confidence.
Accredited Ethical Member (AEM)
A designation from the International Colored Gemstone Association (ICA) given to members who commit to the ICA Code of Ethics, transparent treatment disclosure, and responsible sourcing standards. Caram has been an AEM since 1985.
Alexandrite
A rare variety of chrysoberyl that shifts color from green in daylight to red under incandescent light. Historic Russian Ural Mountain alexandrites are the benchmark; modern stones above one carat with strong color change are exceptionally scarce.
Asscher cut
A square step-cut with cropped corners and broad facets, designed to emphasize clarity over fire. Particularly suited to emeralds and finer-clarity sapphires.
Asterism
The optical phenomenon producing a star pattern across a gemstone's dome — most commonly seen in star sapphires and star rubies. Caused by parallel inclusions reflecting light in distinct rays.
Beryl
The mineral family that includes emerald, aquamarine, morganite, heliodor, and goshenite. Each variety is defined by its trace coloring elements.
Bespoke
A jewel made to commission, designed and crafted specifically for one client around a chosen stone, a recovered heirloom, or an original brief.
Birthstone
A gemstone traditionally associated with a calendar month — sapphire for September, ruby for July, emerald for May, and so on. Many birthstones are also fine collector gems, though not all are equally suited for daily wear.
Cabochon
A gemstone cut in a smooth, rounded dome rather than faceted. Used for gems that display optical effects best in dome form — star sapphires, cat's eye chrysoberyl, opals, and emeralds with notable color saturation.
Carat
The unit of weight for gemstones — one carat equals 200 milligrams. Higher carat weight at the same quality grade increases value disproportionately because larger stones are rarer.
Cat's eye
An optical effect where a single sharp band of light moves across the surface of a polished dome gemstone. Cat's eye chrysoberyl (cymophane) is the most prized example; similar effects can also occur in tourmaline, apatite, and certain quartz varieties.
Certificate
A laboratory document describing a gemstone's measurable characteristics: variety, weight, dimensions, treatments, and sometimes origin. Issued by independent gem labs such as SSEF, Gübelin, GRS, GIA, or AGL.
Clarity
A measure of internal and external inclusions in a gemstone. Standards vary by gem species: rubies and sapphires are evaluated against high clarity expectations, while emeralds — which routinely contain "jardin" — are evaluated more leniently.
Color stability
A gemstone's tendency to retain its color under different lighting and environmental conditions. The GRS color stability system rates sapphires from Type 1 (fully stable) to Type 6 (UV-reactive). Stability matters most for daily wear.
Corundum
The mineral family that includes ruby and sapphire — chemically aluminum oxide. Color variations across corundum (red, blue, pink, yellow, padparadscha, etc.) result from different trace elements.
Cushion cut
A square or rectangular faceted shape with rounded corners and large facets. A traditional favorite for colored gemstones — particularly Burmese rubies and Kashmir sapphires — because it preserves carat weight while showing color depth.
Demantoid garnet
A rare green variety of andradite garnet, prized for exceptional dispersion (fire). Russian demantoids — historically the standard — often show characteristic "horsetail" inclusions of byssolite. Today, Namibian and Madagascan demantoids are also significant.
Dichroism
A gemstone's ability to display two different colors when viewed from different angles. Tanzanite, for example, shows violet-blue from one direction and red-brown from another. A property of certain colored gem species; not present in all.
Dispersion
A gemstone's ability to break light into spectral colors — the "fire" you see in faceted stones. Diamond is the most famously dispersive gem, but demantoid garnet, sphene, and zircon also display high dispersion.
Emerald cut
A rectangular step-cut with cropped corners and broad facets, designed to showcase color and clarity. Named for its traditional use on emeralds, but used on sapphires, aquamarines, and other gems where clarity rewards open viewing.
Emerald
The green variety of beryl, colored by trace chromium or vanadium. Colombian emeralds (Muzo, Chivor, Coscuez) are the historic benchmark; Zambian, Brazilian, and Madagascan sources are also significant. Most emeralds receive oil treatment to enhance apparent clarity.
Fancy color
A gemstone of unusual color for its species. Most commonly applied to diamonds (fancy yellow, fancy pink, fancy blue) but also used for sapphires in non-blue colors (yellow, pink, padparadscha, green).
Fluorescence
A gemstone's tendency to glow under ultraviolet light. Significant in evaluating Burmese rubies (which often fluoresce strongly red) and in identifying treatments. Reported on most modern lab certificates.
Four C's
The traditional framework for evaluating diamonds — color, clarity, cut, carat. Adapted for colored gemstones with the addition of origin and treatment as primary value drivers.
GIA (Gemological Institute of America)
A major independent gemological laboratory and educational institution headquartered in Carlsbad, California. Issues internationally recognized gemstone reports and provides gemological training (the GG credential).
Gübelin Gem Lab
A leading Swiss gemological laboratory, founded in 1923, known for rigorous origin determination on rubies, sapphires, and emeralds. Its reports are particularly valued at auction.
GRS (Gem Research Swisslab)
A Swiss-based gemological laboratory specializing in colored gemstones, particularly rubies, sapphires, and emeralds. Notable for its color terminology framework (e.g., "Royal Blue," "Vivid Red") and color stability classification.
Hardness
A gemstone's resistance to scratching, measured on the Mohs scale from 1 (talc) to 10 (diamond). Sapphire and ruby (9), spinel (8), alexandrite (8.5), emerald (7.5), and tanzanite (6.5) span the typical range. Hardness influences suitability for everyday wear.
Heat treatment
Controlled heating of a gemstone to improve color, clarity, or appearance. Standard practice on most commercial sapphires and rubies; less common (and not always accepted) on emeralds, spinels, and some other species. Disclosure is required under gemological ethics.
Hue
The basic color of a gemstone — red, blue, green, yellow, etc. One of three components of color, alongside tone and saturation.
Inclusion
An internal feature of a gemstone — a fingerprint of its natural formation. Some inclusions are valued (jardin in emeralds, silk in sapphires); others detract from clarity. Inclusions also help identify origin and confirm natural (versus synthetic) formation.
Jadeite
The more valuable of the two jade types (the other is nephrite). Imperial green jadeite from Myanmar is among the most valuable gemstones in the world by weight. Often associated with Chinese collecting traditions.
Jardin
A French word meaning "garden," used to describe the characteristic internal inclusions of emeralds — fine, leafy, or wispy patterns that confirm a natural emerald and rarely reduce value when typical for the
species.
Kashmir sapphire
A blue sapphire from the historic Kashmir deposits in the Indian-controlled portion of the Kashmir region. Mined briefly in the late 19th century before reserves were essentially depleted. Known for an unusually velvety blue with cornflower undertones. Today, "Kashmir" on a lab report commands a significant premium.
Lab report
An independent gemological document — see Certificate. Different labs use different formats, but most include species, weight, dimensions, treatments observed, and (sometimes) origin opinion.
Mohs scale
The hardness scale developed by Friedrich Mohs (1812) for ranking minerals by scratch resistance. See Hardness.
Mozambique ruby
A ruby from the Mozambique deposits, particularly the Montepuez region. Mozambique now produces a significant share of fine rubies on the market; quality ranges from light pink to fine pigeon's blood.
Origin
The geographic source of a gemstone — Burma vs. Mozambique for rubies, Colombia vs. Zambia for emeralds, Kashmir vs. Sri Lanka for sapphires. Determined by inclusion patterns, trace elements, and laboratory analysis. Influences value but does not determine quality on its own.
Padparadscha sapphire
A rare sapphire variety with a delicate pink-orange color, holding both hues in balance. The name comes from the Sinhalese word for lotus blossom. Sri Lankan and Madagascan stones are the principal sources. Untreated padparadschas are exceptionally rare.
Paraíba tourmaline
A neon blue-green tourmaline colored by copper, originally discovered in the Paraíba state of Brazil in 1989. Now also mined in Nigeria and Mozambique. Among the most valuable tourmalines and most distinctive colored gemstones.
Parure
A coordinated jewelry suite — historically including necklace, earrings, bracelet, brooch, and tiara — designed to be worn together. A traditional luxury form increasingly rare today.
Pavé
A setting style where many small diamonds or colored gems are set close together, paving the surface. Used to enhance the brilliance of a central gem.
Pigeon's blood
A trade term for the most prized ruby color — a vivid red with a slight bluish or violet undertone, often
associated with the finest Burmese rubies. Now also used (sometimes contentiously) for top-quality Mozambique rubies.
Pleochroism
A gemstone's ability to display different colors when viewed from different directions. Stronger version of dichroism. Tanzanite, alexandrite, and tourmaline display notable pleochroism.
Provenance
The traceable history of a gemstone — where it was mined, when it was cut, how it has been bought and sold, and any documented owners. Historical provenance (e.g., from royal or famous collections) can dramatically affect value.
Refractive index
A measure of how much a gemstone bends light. Used in laboratory identification. Different gem species have characteristic refractive indices — diamond 2.42, sapphire 1.76, emerald 1.58, and so on.
Royal Blue
A trade color description, codified by GRS, for the finest blue sapphires — saturated, slightly violet, and vivid. Often used to describe top Burmese or Sri Lankan blue sapphires.
Saturation
The intensity or strength of a gemstone's color. One of the three components of color alongside hue and tone. A highly saturated stone shows its color vividly; an under-saturated one appears washed out.
Setting
The metal framework that holds a gemstone in a finished jewel. Common settings include prong, bezel, channel, pavé, and tension. Setting choice affects both the gem's appearance and its protection during wear.
Silk
Fine needle-like inclusions in corundum (ruby and sapphire), often composed of rutile. Light "silk" can soften a stone's appearance and is considered a sign of natural origin. Heat treatment can dissolve silk and is detected by labs.
Spinel
A separate mineral species from corundum, historically confused with ruby — many crown jewels labeled "ruby" are in fact spinel. Available in red, pink, blue, cobalt blue, lavender, and gray. Typically untreated, which is increasingly valued by modern collectors.
SSEF (Swiss Gemmological Institute)
A leading Swiss gemological laboratory headquartered in Basel, known for origin determination and pioneering research. Particularly authoritative on ruby, sapphire, and emerald origin questions.
Step cut
A faceted cut style with rectangular or parallelogram facets arranged in steps. Emerald cut, baguette, and Asscher cut are all step cuts. Favored for stones where clarity and color depth are more important than brilliance.
Suite
A matched set of fine jewelry — typically a necklace and earrings, sometimes including a ring or bracelet — designed to be worn together. Less formal than a parure but with similar coordination of materials, color, and design.
Tanzanite
The trade name for blue-violet zoisite. Mined only near Mount Kilimanjaro in Tanzania — a true single-source gemstone. Almost always heat-treated to enhance color. Softer than sapphire (6.5 Mohs).
Tone
The lightness or darkness of a gemstone's color. One of three components alongside hue and saturation. Most fine colored gemstones sit in the medium-to-medium-dark tone range.
Tourmaline
A diverse mineral family covering more colors than any other gem species. Notable varieties include rubellite (red-pink), indicolite (blue), Paraíba (neon copper-bearing), and watermelon (bicolor pink-green).
Treatment
Any process applied to a gemstone after mining to improve color or clarity. Common treatments include heat, oil (emerald), beryllium diffusion (sapphire), irradiation, and clarity enhancement. Disclosure is required.
Tsavorite
A rare green grossular garnet, discovered in East Africa in 1967. Distinguished from emerald by greater hardness, no need for oil treatment, and a vivid, lively green. Fine tsavorites above 5 carats are exceptionally rare.
Type 3a / Type 3b
GRS color stability classification for sapphires. Type 3a sapphires are color-stable under standard wearing
conditions but may show minor variation under specific lighting. Often misunderstood — a Type 3a is a stable, accepted classification, not a defect.
Untreated
A gemstone that has received no enhancement after mining. Untreated fine rubies, sapphires, and emeralds are significantly rarer than treated counterparts and command premium prices. Confirmed only through laboratory examination.
Vivid
A trade descriptor for color saturation at the highest level — a vivid red ruby, a vivid blue sapphire. Used inconsistently across labs and dealers; meaning is most reliable when tied to a specific lab's color
reference set (e.g., GRS Vivid Red).
Yellow sapphire
A yellow corundum, colored by trace iron. Sri Lanka and Madagascar are major sources. Heat treatment is common to enhance color. Less expensive than blue sapphires of similar quality but increasingly valued for collector pieces.
Zambian emerald
An emerald from the Zambian deposits, particularly the Kagem mine. Distinguished by typically cleaner clarity and slightly cooler, more bluish-green tones compared to Colombian emeralds. Now a major share of the fine emerald market.