In a postcard Robert Proctor writes: Here I am in this remote corner of Sicily tracking down the origins of Agate, as mentioned by Theophrastus in 300 B.C. Lonely here, doing sign language with farmers clutching bunches of asparagus. Found that historians and agateers have made a big mistake—Agate River is 100 miles west of where everyone thinks. Which is why my luggage is so heavy.

Back in his office in the history department at Penn State, Proctor elaborates. One stout farmer, capped with a beret, brandished his asparagus and shouted. It sounded, Proctor thought, like, Are you stealing my cherries? Proctor lifted his hands, full of agates, and the farmer laughed. Oh, rocks. Just rocks. Take all you want. He laughed and laughed. "That's how most people see them," Proctor says. "Just rocks."

He pauses, picks a red, egg-shaped rock off his desk. "I think of them as sleeping until I pick them up," he says.

Proctor has created a career as a historian questioning what we know and don't know. In a series of books on the relationship between science and public policy, he wonders, Why haven't we asked different questions? What are the blinkers we, as a thinking people, put on knowledge? He calls his approach, only half jokingly, "agnatology," or the "science of ignorance" (coined by a linguist friend from agnosis, "not knowing"), and he has applied it to topics as varied as the war on cancer, the concept of race, and the Nazis' health campaigns.

Agates are "an excellent object" for this sort of study, he argues. As he writes in his book-in-progress, Agate Eyes: A Lapidary Journey, "By contrast with diamonds or asbestos or granite or the minerals we burn for fuel, the lowly agate is the victim of scientific disinterest, the same kinds of structured apathy I have elsewhere called ‘the social construction of ignorance.' Agates seem to fall outside the orbit of geological knowledge, and therefore tend to be regarded—if at all—as geological accidents or oddities not really deserving systematic study."

We know they are formed by silica and water, kin to chert, flint, opal, and rhyolite. But how are their elaborate bands of colors created, how do their intricate patterns arise? We don't know "whether they form hot or cold, over days or even minutes, or over millions of years," says Proctor, accreting like pearls (probably not) or solidifying from a gel or slurry (also not likely). Peter Heaney, a geoscientist at Penn State, Proctor notes, has a new theory that explains some aspects of agate growth (see sidebar); even so, we're not that much farther along than the ancient Greeks, who thought agates were ice turned to stone.

But don't let Proctor fool you. It's not geological knowledge he's after (although he is curious), it's rocks. His office has a few choice specimens, skillfully cut and polished, neatly arranged. At home, his living room sports a nook with glass shelving where well-lighted rocks are displayed. And a basket or two of rocks on the piano. And some on the chest in the foyer. And some on the floor. Then there are the rejects and also-rans under the shrubbery outdoors. And heaven help you if you wander into the basement room where he does his cutting and grinding and polishing (where he worries what the rock dust is doing to his lungs and where, sometimes, he is stricken with "agate paralysis," knowing that every time he grinds a layer off a rock to polish it further he is "destroying incredibly beautiful pictures") and you find the boxes and boxes of discards that lure like treasure chests: perhaps there's a beauty here he's overlooked?

My personal love-affair with agates dates from my childhood years, he writes in Agate Eyes. Of family vacations out west: I remember being convinced that the hills were full of gold and precious gems, and that only my parents' recalcitrance was preventing us from striking it rich. My mom says I wanted to stop and pan for gold in every creek we passed, and I will never forget the frustration of having to pass up nature's bounty. Then there were the enchanting mysteries of Chet's Rock Shop outside Laramie, Wyoming, where we were stranded for three days with a broken axle; my brother and I gathered up many of the gemstone scraps Chet had discarded, in the dust under his rocksaw—some of which I still have today: the apple green float jade, the Montana slab with red-tipped black dendrites, bits of a Priday Ranch thunderegg with pink and yellow plumes. . . . I remember wondering whether there were agates at the bottom of the ocean and on distant planets, whether there could ever be an end to all this treasure, how much I could gather in the time I would have on earth.

Now, gathering rocks off his office windowsills and shelves, he can say exactly where each was found (often by him). They have names, all of them. With a cataloguer's mind and the historian's flair for context, Proctor tells the story of each one.

"It's a different kind of knowledge, a hobby knowledge, an amateur knowledge," he explains, "amateur in the literal sense, of loving the thing. You could also call it connoisseurship.

"It's local knowledge. Agates are very different place to place. They are very profoundly local. If I show you a diamond, you can't say where it came from. But if I show you an agate, you can." As he writes, Agateers can often tell at a glance from where in the earth a particular stone has come, sometimes within a hundred feet or so. Even two very similar agates, with branching fronds and tendrils, a dendritic pattern. "Khazakstan has a dendritic agate, for example, and Montana has a dendritic agate," Proctor says, "but you can tell them apart." The colors, the widths and wiggles of the color bands, are distinctive. "There are at least a thousand different types of agates—;a thousand localities. That's the ultimate knowledge form: locality."

This "local knowledge" is not the same as indigenous knowledge: Agateering isn't like ethnobotany; you don't seek out the elders, the keepers of tribal lore, to help you find useless rocks. Only other rockhounds really care. "It takes agate eyes to see them," Proctor says. "People living right there often can't see them. You have to know where to look, but also when and how—with or against the light, in high or low water. A great deal of skill goes into finding them. You have to know what you're looking for and where to go to find it."

Proctor has gone agate-hunting in Brazil, Australia, Scotland, Germany, and "all over" the United States, including the Yellowstone River in Montana, Minnesota, southern California, Arizona, and Texas. Uncut, agates are unimpressive, rough and dull. They form in any hole, from a volcanic bubble to a dinosaur bone. In limestone ledges and seams in rock. The hollows of ancient snails. Eggshells. The cavities of corals. They can be pea-sized or weigh many thousands of pounds. Not always, but often, they are almond-shaped or round. Cut open, they reveal striations of color, pictures and patterns in brilliant hues. Agates are the most beautiful of stones, I believe, Proctor writes, because they are the most diverse of all stones. No two are identical.

Which, ironically, is why they are not as valuable as diamonds. In a chapter called "Anti-Agate: The Great Diamond Hoax and the Semiprecious Stone Scam," Proctor turns his historian's mind to the economics of gemstones, precious and semi-precious. Diamonds are expensive because they are plentiful and ugly, he writes. Agates are cheap because they are rare and beautiful.

It's not only that agates have no real economic uses. (They made good bookends, or handles for umbrellas; diamonds make drills and cutting tools.) According to Proctor, "It was social and political events that rocketed diamonds to the top of the gemstone hierarchy." In particular, it was the concept of the diamond engagement ring.

"How did we come into a world where the majority of women in the richer parts of the globe expect a diamond as proof of engagement, the modern version of bride-price?" Proctor characteristically answers himself within the question: It is a bride-price, proof of a man's worthiness.

When diamonds were discovered in South Africa in the late 1800s, the market for jeweled thrones and crowns of state was soon flooded. As the world's annual production [of diamonds] rose by a factor of ten, and then a hundred, and then by literally thousands, the question became: How do you avoid a plummet of prices? The genius at De Beers, the diamond cartel, who proposed the mass-market diamond engagement ring remains anonymous, but the idea resulted in one of the most successful propaganda campaigns the world has ever seen, Proctor writes. Whereas in 1880 almost no one in the U.S. owned a diamond engagement ring, by the 1920s it was expected that a middle-class bride would receive one. By the 1950s even laboring-class brides were expected to be able to display a diamond—thanks to the newfound formula of De Beers, according to which an engagement ring should cost a bridegroom two months of his salary, before taxes.

The idea worked, Proctor explains, because the time was right. Not only does a diamond look its best under bright electric light, just then becoming widespread, but at the turn of the century annual style changes—in clothes and cars—were catching on; the consumer culture was inventing itself. A diamond, on the other hand, was "forever." It stood for tradition: You don't update your diamond, or turn it in for a newer model, Proctor writes. Diamonds were supposed to be as permanent as your marriage; abandoning your ring would be like abandoning your marriage.

This new "tradition" intersected with two other social changes: the rise of cross-ethnic marriages and a change in the legal status of "breach of promise." When two ethnic marriage traditions conflicted, the diamond cut through all of these hoary rituals, and eventually reduced the process to a simple question of mathematics: How much do you earn? The ring became the bride's insurance plan. Because of changes in the legal meaning of "private space" and "familial affairs," courts that had once granted hefty sums to jilted brides became reluctant to enforce so-called ‘breach of promise' legislation. Women suffering broken engagements had previously been entitled to sums equivalent to settlement of divorce. Now they got to keep the ring.

Diamonds could play these roles because they are, essentially, a form of currency. They are "bland." They are "the Velveeta cheese of the gemstone kingdom," Proctor says. They dazzle and sparkle, he writes, but at the end of the day they all look pretty much alike. . . . They are, in fact, the world's most homogeneous stones. They are the "anti-agate." There is no way to distinguish a diamond from South Africa and one from Sierra Leone (something the United Nations would like to do, since "conflict diamonds" smuggled out of Sierra Leone are underwriting a brutal regime). Practically, this homogeneity meant they could be graded and sold by lot, their value standardized and agreed upon worldwide.

But diamond "as a girl's best friend," was not the only factor responsible for it becoming the number one stone. There were more subtle, and more sinister, forces at work, Proctor writes. One was the new scientific distinction made between "rocks" and "minerals" in the mid-1800s. A mineral was pure; a rock was a mixture. The idea was patterned on the concept of chemical elements. Mineralogy becomes essentially a subbranch of chemistry, Proctor writes, and the search is launched to identify pure "mineral species" comparable to organic species. The rhetoric of purity is central in the effort. "Species" (and races) were supposed to be kept separate. Agates being rocks—mixtures of minerals—they were "boundary crossers," in today's jargon. To a late 19th-century scientist, they were "impure."

For Proctor, whose critical eye has been for so long trained on Nazi Germany, there's more than just rocks involved. Ideas do not develop in a vacuum, he writes. The racial doctrines that would do so much damage in the 20th century were just beginning to be formulated in the middle of the 19th, and there is arguably a certain parallel development in mineralogy and gemmology, leading to the elevation of "pure" minerals over "mixed" rocks—which culminates in the invidious distinction between precious and semi-precious gems, the former clear and chemically pure, the latter mixed and chemically suspect. . . . The very diversity that made an agate beautiful became an insult to the eye of the mineralogist.

Proctor was on his way to deliver a paper, "Agates in World History," at the First International Agate Conference in Wurms, Germany, when he detoured to Sicily to find the original river named Acate, or Agate.

"I looked for three days," he says, not for the river, but for the rocks that, as he writes in Agate Eyes, are windows onto the world, gemstone jazz, a child's delight, poetry in stone.

"I talked to roadbuilders, teachers, gardeners. I found no agates. I don't think anyone has ever found agates in this river. But 100 miles west is another river that I did find agates in. Tons of agates and jaspar and banded chalcedony, which they were calling agate."

After a two-day stopover at home, he collected his family (historian Londa Schiebinger and their two boys) and flew to Jamaica for a week's vacation where, of course, he searched the rivers for agates. "Agates are always found in beautiful places," he says, "so it's not hard to convince the family to take vacations there." But, "there are hundreds of rivers in Jamaica, and each has a different agate." After a day or two, "Londa thought we had enough agates, but I thought we were just scratching the surface."

From Sicily, he had brought 30 or 40 pounds of agates; from Jamaica he carried over 100 pounds.

Geologists tend to study ugly rocks, rockhounds covet beautiful ones. . . . The agateer's focus is on beauty, texture, and proportion; there is the thrill of the hunt and the pleasure of the polish. The lapidary is not a geologist, for geology is (now) a profession while lapidary is (still) a passion.

"Galileo said we collect stones because we fear death," he says, turning the red egg-sized stone over in his hand to show a polished face that's a maze of brick red and blue and crystalline gray. "I love that part about these stones, that they are millions of years old and could last millions more.

"And think of the exoagates! The universe may be full of agates, and they would be different on each planet.

"That's incredibly frustrating: I'll never see them. No intelligent being will ever see them or love them or cut them."

A few days later, he sends a note to clarify that thought. The conditions for the evolution of life may be close to those for the formation of agates (water at low temperatures, etc.), he writes, so maybe there are intelligent creatures out there finding, cutting, and polishing their own agates. I hope so.

Robert N. Proctor, Ph.D., is professor of history, College of the Liberal Arts, 312 Weaver Bldg., University Park, PA 16802; 814-863-8943; rnp5@psu.edu.