Rocks, minerals and crystals — The World, with the Evidence

A huge, round hole with vertical walls, filled with blue water at the bottom, surrounded by bushes. — The “Big Hole”, an open-pit diamond mine dug at Kimberley, South Africa (photograph by Rudolph Botha, 2005). Rudolph Botha, CC BY-SA 3.0, source

The rarity of a stone is not always a fact of nature.

It can be organised, and an entire family tradition can have a date of birth.

Four words, and a manufactured market

There is a stone whose value and perceived rarity owe everything to the control of supply by the De Beers cartel and to an advertising campaign orchestrated by the N. W. Ayer agency.¹

In the late 1940s, the copywriter Frances Gerety came up with four words late one night: “A diamond is forever”. At the time, nobody made much of it, and colleagues even criticised its grammar. Yet the line would go on to become one of the most effective slogans in the history of marketing.²

What the slogan really does

It reads as a sentimental phrase. In reality, it works on three levels at once:

The apparent meaning — It links the diamond to the eternity of romantic commitment.
The economic lock — It actively discourages resale. If a diamond is “forever”, it stays in the family. Without a second-hand market to loosen supply, the price of new stones faces no competition.
The social imperative — It makes this purchase a unique, irreversible and obligatory act.

What the agency itself said

The most interesting part comes from its own reports.

The agency explained that it had had to invent an entirely new form of advertising, because it had none of the things normally used:³

There was no direct sale to be made. There was no brand name to be impressed on the public mind. There was simply an idea — the eternal emotional value surrounding the diamond.⁴

Selling an idea, not a product. The phrase should be taken literally: the agency was not trying to make people prefer one brand to another. It was trying to establish a self-evident truth — from which any seller would then benefit.

How a self-evident truth is established

The methods are documented, and look nothing like advertisements.

Through schools. The agency organised lectures in educational establishments, reaching thousands of girls in assemblies and classes.
Through the news. From 1946, it supplied one hundred and twenty-five leading newspapers each week with descriptions of the diamonds worn by film stars. This was not advertising: these were articles.
Through example. It commissioned portraits of engaged young people from high society, intended to serve as role models for more modest families.⁵

None of this looks like an advertisement. That was precisely the aim: for the message to arrive not through the door of advertising, but through those of the school, the newspaper and admiration.

The result can be measured: as early as 1941, the agency reported that diamond sales had risen by 55% in the United States since 1938, reversing a continuous decline.⁶

Proof by resale

There is a simple way to find out whether an object is really worth the price paid for it: try to resell it.

That is the very title of the standard investigation on the subject: “Have You Ever Tried to Sell a Diamond?”

The documented answer is no. A private individual who takes their stone back to a jeweller gets only a fraction of the purchase price — because the trade buys back only at the wholesale price, far below the retail price.⁷

The slogan and this fact hold each other up. As long as no one resells, no one finds out.

The sign that betrays an invention

The “rule” that an engagement ring should cost two months’ salary is no ancestral custom: it was devised from scratch by the N. W. Ayer agency in the 1980s.

How this made-to-measure rule was built is easy to verify: De Beers advertisements first suggested one month’s salary, then two.⁸

When a “traditional” rule changes its amount from one advertisement to the next, the commercial construction becomes obvious.

The technological denouement

Synthetic (or laboratory-grown) diamonds have the same crystal structure and nearly the same chemical and optical properties as stones extracted from the ground. Gemmological laboratories grade them to exactly the same standards.⁹

The only difference is how long they take to form: a few weeks in a reactor (via the HPHT or CVD processes) compared with more than a billion years in the Earth’s mantle.

The emergence of low-cost synthetics has broken the cultural and commercial monopoly of natural diamonds, demonstrating that perceived rarity was nothing but a product of advertising engineering.

Minerals, crystals and rocks

A mineral meets a strict scientific definition: a naturally occurring, homogeneous solid substance with a defined chemical composition and an ordered atomic structure.¹⁰

A rock is not a mineral, but an assemblage of minerals (granite, for example, is an assemblage of quartz, feldspar and mica).
A crystal is the state of matter in which atoms are arranged periodically and symmetrically in all three dimensions of space.¹¹

The hierarchy is as follows: atoms arrange themselves in ordered lattices, which form the crystals of minerals; minerals come together into rocks. A sandy beach, a pebble, a cliff and a kitchen worktop are all assemblages of this kind.

The three families of rocks

All the rocks on the planet fall into three families, according to how they formed. This is the basic classification of geology, and it can be summed up in three verbs: to cool, to settle, to transform.

Igneous rocks are born from magma that cools. If it cools slowly, at depth, the crystals have time to grow and become visible to the naked eye: this is granite. If it cools abruptly on contact with air or water, the crystals remain tiny: this is basalt, the rock of lava flows.
Sedimentary rocks form by accumulation. Debris torn away elsewhere by erosion, or the shells of marine animals, settle in layers at the bottom of the water, then become compacted under the weight of what builds up above. Sandstone comes from sand, limestone from shells, coal from plants. It is in these rocks that most fossils are found, for a simple reason: the other two families generally go through temperatures that destroy living remains.¹²

They make up only a small share of the crust’s volume, but they cover about three quarters of its land surface. That is why they are, by far, the rocks most often encountered — and why the history of life is read almost entirely in just one of the three families.

Metamorphic rocks are former rocks transformed in place, without melting, by high pressure or high heat — most often because they ended up buried during a plate collision. Limestone becomes marble, clay becomes slate.

Nothing is permanent

A rock from one family can become a rock from another. A granite exposed to the air breaks down into sand, the sand settles and compacts into sandstone, the sandstone buried beneath a mountain range is transformed into quartzite, and the quartzite carried deep enough eventually melts and becomes magma again.

This journey is called the rock cycle. It follows no fixed order: a rock can skip stages, or travel the same route several times. It is measured in millions of years, which explains why it is never seen unfolding — only snapshots of it are observed, scattered across the landscape.¹³

What metal costs

The extraction of precious stones and metals never escapes its human and ecological cost.

Mining history, from silver production at Potosí under the Spanish Empire to the modern extraction of rare earths and coltan for the electronics industry, follows the same recurring pattern: massive energy consumption, population displacement and the exploitation of forced labour.¹⁴

Note 1

This enabled De Beers to stockpile diamonds, strictly control the release of stones to the global market, and effectively control prices – thereby creating an illusion of diamond scarcity worldwide. Meanwhile, De Beers sought to enhance global demand for diamonds. In 1946, the company hired NW Ayer, a Philadelphia-based advertising agency, which one year later came up with the legendary slogan […]

Darley, George Charles, “How the diamond engagement ring was invented – and sold around the world”, Al Jazeera, 14 September 2025

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Note 2

The "A Diamond is Forever" tagline was written in 1949 by Frances Gerety, a woman copywriter at Ayer from 1943 to 1970.

Smithsonian Institution, National Museum of American History, Archives Center, N W Ayer Advertising Agency Records, NMAH.AC.0059, inventaire en ligne (fonds consultable sur place), open access

When Frances first come up with the line that becomes the line of the century, the men in the agency start picking at its grammar. […] And it was really not a big deal in the moment. […] So she remembered late one night when she had finished her work, you know, at 3 in the morning.

NPR, Here and Now, “The Ad-Woman Who Made Diamonds ’Forever’”, entretien de Robin Young avec J. Courtney Sullivan, 2013, transcript open access

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Note 3

its campaign had required the conception of a new form of advertising which has been widely imitated ever since