Birthstone · Month

May: emerald

Emerald holds May in every list, and it is the stone that best rewards knowing a little chemistry. Its green comes from chromium meeting beryllium, a geologically unlikely pairing, and the same conditions that produce the colour also fracture the crystal, which is why nearly every emerald on earth has been oiled.

At a glance

The month of the stone that is almost always oiled, and whose green comes from an unlikely chemical accident.

Modern list (1912 onward)
Emerald
Traditional European lists
Emerald
Older alternatives cited
Agate, chrysoprase
Zodiac signs in this month
Taurus, Gemini
Vedic gems for those signs
Diamond for Taurus, emerald for Gemini (Mercury)
Hardness
Mohs 7.5 to 8, but brittle and fracture-filled

Themes

the vow growth green fracture chromium

The modern answer

Emerald, uncontested across the modern and traditional lists.

Emerald is beryl coloured green by chromium or vanadium. Beryllium concentrates in granitic rocks and chromium in dark mantle-derived rocks, and the two rarely meet. Where they do, usually where hydrothermal fluid from a granite invades chromium-bearing schist, emerald forms, and the violence of that process fractures the crystal as it grows.

That is why the mossy inclusions in an emerald, which gemmologists call the jardin, are accepted as normal rather than treated as flaws. A flawless emerald would be more suspicious than a included one.

The older lists

Traditional lists agree on emerald, with agate and chrysoprase appearing as alternates in some regional versions.

Egypt worked emerald at Wadi Sikait in the Eastern Desert from before 1500 BCE, and those workings were later called Cleopatra's mines. The classical world read emerald as Venus's stone, and Pliny records that lapidaries rested their eyes by looking at emeralds, which is a reasonable observation about colour fatigue rather than a magical claim.

Medieval lapidaries gave emerald a reputation for chastity, holding that it would shatter if the wearer broke a vow, and for revealing whether what was said in its presence was true.

Colombia changed the picture entirely. Muzo and Chivor produced material of a quality Europe had not seen, and Spanish colonial trade moved it in enormous volume to India, where Mughal patrons carved it, and to Europe.

In Ayurvedic tradition emerald is the gem of Mercury, prescribed for intellect, speech and commerce.

What emerald is actually like to own

This is the most demanding stone in the calendar. It is hard at 7.5 to 8, meaning it resists scratching, but it is brittle and pre-fractured, meaning it chips and breaks under impact far more readily than that number suggests.

The overwhelming majority of emeralds are clarity-enhanced with oil, resin or polymer, disclosed by degree from none through minor to significant. Traditional cedarwood oil is reversible; hardened resins are not.

Practical consequences: never an ultrasonic or steam cleaner, never a jeweller's torch without telling them, and expect a daily-worn emerald ring to need re-oiling every few years. Take it off for gardening, gym work and washing up.

Synthetic emerald has been grown since the 1930s and is chemically identical, far cheaper, and honest when labelled.

If you would rather have something else

Chrysoprase is the interesting alternative, since it is green chalcedony coloured by nickel, hardness 7 with no cleavage, and it will survive anything an emerald will not. Frederick the Great had Silesian mines worked for it.

Agate appears in older May lists and is cheaper still.

May covers Taurus and Gemini. Zodiac lists give Taurus emerald, which agrees with the calendar, and Gemini agate or citrine. In Jyotish, Gemini is ruled by Mercury, whose gem is emerald, so a May Gemini gets emerald from two directions at once, while a May Taurus answers to Venus and diamond.

Otázky na zamyslenie

  • What have I promised that I would not want tested?
  • What in my life is beautiful because of its flaws rather than despite them?
  • Where am I treating something fragile as though its hardness protects it?

Frequently asked questions

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