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Guide
Colored gemstones vary widely in hardness, in how they are typically treated, and in how they should be cleaned. This guide covers sapphire, emerald, ruby and several other stones so you know what to expect from each before you buy.
The Mohs scale ranks a mineral’s resistance to scratching from 1 to 10, with diamond at 10. A higher number resists scratching from everyday contact (dust, countertops, other jewelry) better, which is why corundum stones such as sapphire and ruby are common choices for a ring, while softer stones are better suited to a pendant or earrings that see less contact.
Most colored gemstones sold today are treated in some way to improve color or clarity, and many treatments are standard, stable and expected across the trade. What matters is that a treatment is disclosed, since it affects both how a stone should be cared for and how it is fairly priced against an untreated stone of similar appearance. We disclose known treatments on the product page for every colored stone we sell.
Origin, the country or region a stone was mined in, can affect a stone’s value independent of its other characteristics, particularly for sapphire and ruby, where certain origins carry a reputation in the trade. Where origin has been determined by an independent laboratory, it is listed on the stone’s report and on the product page.
| Stone | Hardness | Daily wear | Care |
|---|---|---|---|
| Sapphire | 9 on the Mohs scale | Among the most durable colored stones available and a common choice for a ring worn daily, second only to diamond in hardness. | Tolerates an ultrasonic cleaner in most cases, though a filled or fracture treated stone should be cleaned only by hand. |
| Emerald | 7.5 to 8 on the Mohs scale | Harder than quartz but naturally included, which makes emerald more prone to chipping along an inclusion than its hardness number alone would suggest; better suited to earrings and pendants than to a ring worn hard every day. | Clean only by hand with mild soap and a soft cloth. Avoid ultrasonic cleaners, steam cleaners and prolonged contact with household chemicals. |
| Ruby | 9 on the Mohs scale | As durable as sapphire, since both are corundum, and equally suited to daily wear when the setting protects the stone's edges. | Tolerates an ultrasonic cleaner if untreated or only heat treated; a glass filled stone should be cleaned by hand only. |
| Aquamarine and other beryls | 7.5 to 8 on the Mohs scale | Reasonably durable for occasional wear; more prone to surface abrasion over years of daily contact than corundum or diamond. | Generally tolerates an ultrasonic cleaner if free of visible inclusions reaching the surface; hand cleaning is the safer default. |
| Tanzanite, opal and other softer stones | 5.5 to 7 on the Mohs scale | Softer and, in the case of opal, more sensitive to impact and to changes in humidity; best suited to earrings, pendants or occasional wear rather than an everyday ring. | Clean by hand only, avoid ultrasonic cleaners and sudden temperature changes, and store separately to prevent scratching from harder stones. |
Among the most durable colored stones available and a common choice for a ring worn daily, second only to diamond in hardness.
Treatments: The large majority of sapphires on the market are heat treated to improve color and clarity, an accepted and stable treatment across the trade. Less common treatments, such as diffusion or clarity enhancement with a filler, affect durability and value differently and should be disclosed separately.
Care: Tolerates an ultrasonic cleaner in most cases, though a filled or fracture treated stone should be cleaned only by hand.
Harder than quartz but naturally included, which makes emerald more prone to chipping along an inclusion than its hardness number alone would suggest; better suited to earrings and pendants than to a ring worn hard every day.
Treatments: Nearly all emeralds are treated with oil or resin to fill surface reaching inclusions and improve apparent clarity. This is standard practice and expected in the trade, but it means an emerald should never be cleaned ultrasonically or with strong solvents, which can strip the filler.
Care: Clean only by hand with mild soap and a soft cloth. Avoid ultrasonic cleaners, steam cleaners and prolonged contact with household chemicals.
As durable as sapphire, since both are corundum, and equally suited to daily wear when the setting protects the stone's edges.
Treatments: Most rubies are heat treated, and some are also clarity enhanced with glass or another filler to reduce the visibility of inclusions. A glass filled ruby is significantly more fragile and should be disclosed and priced accordingly.
Care: Tolerates an ultrasonic cleaner if untreated or only heat treated; a glass filled stone should be cleaned by hand only.
Reasonably durable for occasional wear; more prone to surface abrasion over years of daily contact than corundum or diamond.
Treatments: Most aquamarine is heat treated to shift color toward a cleaner blue; this treatment is stable and permanent.
Care: Generally tolerates an ultrasonic cleaner if free of visible inclusions reaching the surface; hand cleaning is the safer default.
Softer and, in the case of opal, more sensitive to impact and to changes in humidity; best suited to earrings, pendants or occasional wear rather than an everyday ring.
Treatments: Tanzanite is almost always heat treated to develop its blue to violet color. Opal is not typically treated for color but can be stabilized or, in the case of doublets and triplets, assembled with a backing, which should always be disclosed.
Care: Clean by hand only, avoid ultrasonic cleaners and sudden temperature changes, and store separately to prevent scratching from harder stones.
If you are choosing between stones for a piece you plan to wear daily, contact client care or book a consultation and we can talk through what will hold up best for your use.