The May birthstone is emerald, the green variety of beryl. It measures 7.5 to 8 on the Mohs scale, comes mainly from Colombia, Brazil, and Zambia, and marks the 20th and 35th wedding anniversaries.
“Some estimates state that 90 percent or more of emeralds are fracture-filled,” according to the Gemological Institute of America (GIA), usually with oils or resins that improve their appearance.
That single fact changes how a May birthstone should be cleaned.
Not every green beryl is an emerald: gemologists disagree on where the boundary lies, and GIA decides by comparing each stone with lab-graded reference stones to judge whether the green is dark and saturated enough to be called emerald. In the UK, chrysoprase is an official alternative May birthstone.
Table of Contents
What is the May birthstone?
Emerald is the official May birthstone on the GIA list; the British list adds chrysoprase as an alternative. The table summarizes emerald’s key properties.
| Property | Emerald (May birthstone) |
|---|---|
| Mineral | Beryl (green variety) |
| Mohs hardness | 7.5–8 |
| Toughness | Fair to good |
| Common treatments | Fracture filling with oils or resins; dyeing |
| Main sources | Colombia (Muzo, Chivor, Coscuez mines), Brazil (Belmont, Capoeirana), Zambia, Pakistan, Afghanistan |
| Wedding anniversaries | 20th and 35th |
| Zodiac signs for May birthdays | Taurus (to about May 20) and Gemini (from about May 21) |
Is there more than one May birthstone?
On the U.S. list, emerald is May’s only birthstone; the UK list also includes chrysoprase, an apple-green variety of chalcedony. The U.S. and UK lists are compared month by month in the Birthstones by Month chart.
May birthstone color: when is green beryl an emerald?
Emerald must show a green that is dark and saturated enough; lighter stones of the same mineral are sold as green beryl.
There is no single industry standard for the dividing line. GIA’s emerald description states that GIA “uses lab-graded comparison stones to determine if the green color is dark enough and saturated enough to be called emerald.”
The table compares emerald with other green May birthstone options and look-alikes.
| Stone | Mineral | Mohs hardness | Typical green | Relationship to May |
|---|---|---|---|---|
| Emerald | Beryl | 7.5–8 | Medium to dark, saturated green to bluish green | Official May birthstone |
| Green beryl | Beryl | 7.5–8 | Light green | Same mineral, below the emerald color threshold |
| Chrysoprase | Chalcedony (quartz) | About 6.5–7 | Apple green, opaque to translucent | UK alternative May birthstone |
| Tsavorite garnet | Garnet (grossular) | 6.5–7.5 | Vivid green | A January birthstone, not a May stone |
Emerald belongs to the same mineral family as aquamarine, the March birthstone; the two differ only in color.
Why emerald inclusions are accepted
Emeralds almost always contain visible inclusions, and the trade treats them as normal for the stone. Eye-clean emeralds are rare, so buyers usually weigh color above clarity when choosing a May birthstone.
Emerald treatments: what May birthstone buyers should know
Most emeralds on the market have had surface-reaching fractures filled with oil or resin to improve clarity.
GIA lists fracture filling and dyeing as common emerald treatments. Fillers can deteriorate over time with heat, light and chemicals, so treated emeralds may need re-oiling.
- Ask whether the emerald is treated and to what degree. Treatment ranges from minor to significant and affects value.
- Request a laboratory report for valuable stones, such as a GIA report, which identifies filling and its extent.
- Plan for maintenance. A jeweler can re-oil a fracture-filled emerald if its clarity dulls.
May birthstone meaning and history
The word emerald comes from smaragdos, ancient Greek for “green gem.” GIA records these historical highlights:
| Period | Emerald in history |
|---|---|
| Ancient Egypt | Cleopatra was famous for wearing emeralds in her royal adornments |
| Ancient Rome | Pliny the Elder wrote that “nothing greens greener” and praised emeralds for relieving eye strain |
| 16th century | Spanish conquistador Francisco Pizarro reportedly took the Atahualpa emerald from the last Inca emperor |
| Colonial Colombia | The Crown of the Andes was made with a 24-carat center emerald and 442 more emeralds |
These associations are historical and cultural; they describe tradition, not gemological properties.
Caring for a May birthstone
Emerald is hard enough for all jewelry but needs gentler care than ruby or sapphire, because most stones are fracture-filled. Follow GIA’s care guidance:
- Clean with warm, soapy water and gentle scrubbing only. GIA calls this “the safest way to clean emeralds.”
- Never use an ultrasonic cleaner. Vibrations can weaken fractured stones.
- Never steam-clean. Steam can make filler leak out of fractures.
- Keep emeralds away from heat. Heat can extend existing fractures.
- Limit exposure to strong light and chemicals, which can break down the oils and resins in filled fractures.
What the May birthstone is not
The May birthstone is often confused with other green stones. The points below separate them.
- It is not any green beryl. Only beryl with a sufficiently dark, saturated green is emerald.
- It is not usually untreated. Fracture filling is standard in the emerald trade.
- It is not the same as tsavorite or peridot. Those are garnet and olivine, the January and August birthstones.
- It is not the only May stone in the UK. Chrysoprase is a British alternative.
Frequently asked questions
What color is the May birthstone?
The May birthstone, emerald, is green to bluish green, with medium to dark, saturated tones. Lighter green beryl is not classed as emerald.
Are most emeralds treated?
Yes. Some estimates state that 90 percent or more of emeralds are fracture-filled, according to GIA, usually with oils or resins.
Can you clean an emerald in an ultrasonic cleaner?
No. GIA advises never to put an emerald in an ultrasonic cleaner; use warm, soapy water and gentle scrubbing instead.
