April Birthstone: Diamond and Rock Crystal, History and Care

Short answer: diamond is the April birthstone. It is pure carbon, the hardest natural material, rated 10 on the Mohs scale. Most natural diamonds are between 1 and 3.5 billion years old, formed deep in the Earth's mantle and carried up in volcanic eruptions. Diamonds are best known colorless but also come in blue, yellow, pink, green and other colors. Britain's birthstone list also gives rock crystal, clear quartz, as an alternative for April.

What is the April birthstone?

On the modern United States list, April has one birthstone: diamond. The British list, kept by the National Association of Goldsmiths, gives diamond and rock crystal. Rock crystal is colorless quartz, a far more affordable clear stone. Diamond is also the gift for the 60th and 75th wedding anniversaries.

What is diamond?

Diamond is carbon with its atoms packed in a rigid crystal structure. It has the greatest number of atoms per unit volume of any substance, which is why it is both the hardest and the least compressible. It also has the highest thermal conductivity of any natural material, and a very high refractive index and optical dispersion, which give a well-cut diamond its brilliance and fire.

Hardness is not the same as toughness. Diamond has a cleavage plane, so a sharp blow in the wrong direction can split it. Diamond cutters use this to cleave some rough stones before faceting them.

How do diamonds form?

Most natural diamonds are between 1 billion and 3.5 billion years old. They formed deep in the Earth's mantle, where, under high pressure and temperature, carbon-bearing fluids dissolved minerals and replaced them with diamond. Much more recently, hundreds to tens of millions of years ago, volcanic eruptions carried them to the surface in rocks called kimberlites and lamproites. Diamonds are almost always found in kimberlites on the oldest parts of continents.

What colors do diamonds come in?

Most diamonds used in jewelry are colorless to near colorless. Because diamond's structure is so rigid, few impurities can enter it, and the main exceptions are boron and nitrogen. Tiny amounts of impurities or defects, about one per million atoms, can color a diamond:

Blue from boron.
Yellow from nitrogen.
Brown from structural defects.
Green from natural radiation exposure.
Pink, purple, orange and red also occur.

A short history of diamonds

Our love of diamonds began in India, where they were gathered from rivers and streams and traded as early as the fourth century BCE. Caravans later brought Indian diamonds to medieval markets in Venice, and by the 1400s they were becoming fashionable among Europe's elite. The first diamond engagement ring on record was given by Archduke Maximilian of Austria to Mary of Burgundy in 1477.

When India's supplies declined in the early 1700s, Brazil became the important source, after gold miners found diamonds in river gravels in Minas Gerais. The discovery of diamonds near Kimberley, South Africa, in the late 1860s began the modern diamond market.

Famous diamonds

The Hope diamond, a 45.52 carat blue diamond, is thought to have come from India's Golconda mining area. It was sold to King Louis XIV of France in 1668, when it was known as the French Blue. It is now at the Smithsonian Institution.
The Cullinan, found at South Africa's Premier mine in 1905, is the largest diamond ever found, at 3,106 carats (621 grams). The pear-shaped 530 carat Cullinan I, the Great Star of Africa, was cut from it and is set in the Royal Sceptre with Cross among the Crown Jewels in the Tower of London.

Where are diamonds mined today?

Diamonds are now mined around the world. Major producers include South Africa, Botswana, the Democratic Republic of the Congo and Russia, which opened its first major mine in 1960. Mining expanded with the Argyle mine in Australia in 1983 and deposits found in northern Canada in the 1990s. Botswana is also a sorting hub, where about 40 percent of the world's rough diamonds are sorted and valued.

What does the April birthstone mean?

The name comes from the Greek adamas, meaning "unbreakable" or "untamed". An anonymous second-century poet claimed that diamond warded off the evil eye, and over the centuries it was credited with bringing strength, beauty and happiness. Today the diamond engagement ring is a near-universal symbol of love and marriage.

These are traditions and beliefs, part of the stone's long history, not properties of the gem.

Lab-grown diamond

Synthetic diamonds are grown from high-purity carbon under high pressure and temperature, or from hydrocarbon gases by chemical vapor deposition (CVD). They are real diamond in chemistry, structure and hardness. Gemologists usually tell natural from synthetic using optical techniques or thermal conductivity measurements, and sellers should always disclose which is which.

Rock crystal: April's other stone

Rock crystal is colorless, transparent quartz. At 7 on the Mohs scale it is much softer than diamond, but it is clear, bright and widely available. The best-known natural "diamonds" of quartz are Herkimer diamonds, double-terminated quartz crystals from New York, named for their clarity and natural facets. They offer an affordable way to own a clear, naturally brilliant April stone.

How do you care for a diamond?

Ultrasonic cleaners are usually fine for diamonds.
For included or treated diamonds, use a lint-free cloth, or warm water, mild soap and a soft toothbrush.
Have the setting checked by a jeweler from time to time.
Store diamonds apart from other gems, which a diamond can scratch.

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