Every gemstone tells a story through its color, structure, and origin. But most buyers walk into a jewelry store with no real framework for evaluating what they’re looking at. That’s where gemological training makes a difference — and it’s exactly why Kenny Phillips earned his credentials through the Gemological Institute of America.
Here’s a straightforward breakdown of what professionals actually look at when evaluating colored stones.
All Gemstones Share Three Traits
Beauty, rarity, and durability. Every gem on the market possesses some degree of all three. Color is the single most important factor in a colored stone’s beauty — it’s the first thing your eye registers, and it’s what drives desire. But rarity and durability determine whether that beauty holds up and holds value over time.
Understanding Color Like a Gemologist
Color isn’t as simple as “it’s blue” or “it’s red.” Gemologists break color into three components: hue (the basic color), tone (how light or dark it is), and saturation (the color’s intensity or strength). A deeply saturated ruby with medium tone commands a premium over a washed-out, overly dark one — even if both are technically “red.”
Then there’s the concept of body color, which is determined by selective absorption — the way a gem’s chemical composition and crystal structure absorb certain wavelengths of light and reflect others back to your eye. Corundum with chromium traces produces ruby. Add iron and titanium instead, and you get sapphire. Same mineral family, completely different stones.
Fine color is the term for the shade the industry prizes most within a given gem species. For example, most buyers prefer a yellowish-green peridot over a greenish-yellow one. Trade names like “Burma ruby,” “Kashmir sapphire,” and “Colombian emerald” exist because certain geographic sources have historically produced the most desirable colors.
Phenomena: When Gemstones Do Something Extraordinary
Some colored stones display optical effects that go beyond simple color:
Play-of-color in opals creates shifting rainbow flashes. Opals are unique — they’re made of tiny spheres rather than crystals, and the way light diffracts through those spheres produces the effect.
Chatoyancy (the cat’s-eye effect) occurs when light concentrates across a narrow band in stones like chrysoberyl. Tilt the stone and watch the band of light shift — gemologists call the best examples “milk and honey” for the way light splits across the surface.
Asterism produces star patterns. Rubies and sapphires commonly display six-rayed stars, while other stones may show four or six rays depending on crystal structure.
Alexandrite is famous for color change — appearing one color in daylight and a different color under incandescent light. Adularescence gives moonstone its signature glow, caused by light scattering through alternating internal growth layers. And labradorescence creates broad, bright color flashes across the surface of labradorite.
Clarity, Cut, and Carat Weight
Clarity in colored stones works differently than in diamonds. Because of the way gem crystals form, most colored stones contain some inclusions. The key question is whether those inclusions affect the stone’s beauty or durability. Only a few gem types — aquamarine, citrine, kunzite, tanzanite, and topaz — are typically expected to be eye-clean (meaning inclusions are only visible under magnification).
Interestingly, some inclusions actually add value. Fine needle-like inclusions called silk can create the cat’s-eye and star effects mentioned above, and certain inclusions help gemologists confirm a stone is natural rather than synthetic.
Cut in colored stones involves shape, style, and finish. Shapes range from the familiar round to fancy shapes like emerald cuts, cushions, ovals, pears, and marquises. Cutting styles include brilliant cuts (facets radiating from center), step cuts (concentric rows of facets), mixed cuts, and cabochons (smoothly domed with no facets). A well-cut colored stone maximizes color saturation and light return while minimizing problems like windowing (a pale, see-through area) or extinction (dark patches that shift as you move the stone).
Carat weight affects value, but not in a simple linear way. The per-carat price often jumps at key weight thresholds, and larger stones of fine quality are disproportionately rare. One metric carat equals 0.20 grams, and total gem weight refers to the combined weight of all stones in a piece.
Durability: More Than Just Hardness
Durability has three components, and confusing them is a common mistake:
Hardness measures resistance to scratching. The Mohs scale ranks minerals from 1 (talc) to 10 (diamond), with corundum (ruby and sapphire) at 9 and topaz at 8. An 8 will scratch anything at its level or softer.
Toughness measures resistance to chipping, cracking, and breaking. Jadeite and nephrite rate exceptional, while topaz and amber rate poor despite topaz’s high hardness score.
Stability refers to how a gem responds to light, heat, and chemicals. Some stones fade with prolonged light exposure. Others can be damaged by common household chemicals.
Treatments: What Every Buyer Should Know
Here’s a reality most buyers don’t consider: the majority of colored stones on the market have been treated in some way. Gem treatment is any human-controlled process that improves appearance, durability, or value. Heat treatment is the oldest and most common. Fracture filling with oils or resins is standard practice for emeralds. Diffusion, irradiation, dyeing, and coating are all used across various gem types.
The critical point: full disclosure is required. The FTC’s Guides for the Jewelry, Precious Metals, and Pewter Industries (first published in 1957, revised in 2010) mandate that sellers inform buyers of any known or suspected treatments. At KP Gems, we believe you deserve to know exactly what you’re buying — treated or untreated, natural or synthetic — before you make a decision.
A good rule of thumb from the GIA: if treatment is possible for a given stone, assume it has been treated unless proven otherwise.
Why This Matters When You’re Shopping
Understanding these fundamentals puts you in a stronger position whether you’re buying, selling, or simply appreciating fine colored gemstones. The five value factors — color, cut, clarity, carat weight, and consumer demand — interact differently for every stone. A gemologist who can walk you through those factors for the specific piece in front of you is worth their weight in, well, gemstones.
Schedule a complimentary private appointment with Kenny Phillips and get expert guidance from a GIA Graduate Gemologist with over 40 years of experience.
Kenny Phillips is a fourth-generation jeweler and GIA Graduate Gemologist. KP Gems offers private, appointment-only consultations in Austin, TX and nationwide via phone and Zoom.
