Dry Storeroom No. 1 (37 page)

Mineralogists appear to be rather a sensible lot compared with biologists and palaeontologists. In my attempts to extract oral history from my former colleagues, it proved remarkably easy to get revelations from those who worked upon organisms—whether living or fossil. Quite a few of these anecdotes involved sexual relations between people who I had no idea had had any relations at all, let alone carnal ones. I was already aware that Dry Storeroom No. 1 was a secret trysting place. That dry old sunfish had witnessed many a lubricious episode. I later heard that the attic floor of the old Entomology Block had mattresses deployed to help the entomologists with their studies of the human genome. It seems that the Dark Room was often locked from the inside because of unforeseen developments. Until I interviewed the protagonists, I had no idea of the lustful tendencies of experts on weevils, toads or brachiopods. By contrast, the mineralogists seem to have been altogether better behaved. This may have something to do with the fact that Mineralogy is the smallest department, and the most overseen. Until quite recently, all the post addressed to the scientists was opened in the Keeper’s office, which was certainly inconvenient for anyone trying to arrange a secret assignation. Mineralogists also tend to be the more mainstream scientists. They are the ones that wear the white coats, and hide away in the basement while reading dials from sophisticated machines. Only a few of them have gone mad, and many of them have lived blameless lives in the single-minded pursuit of mineral excellence.

Minerals do have systematics and taxonomy, just like organisms. Like animals and plants, they are classified into species, although there are far fewer species than in the biological world. The old mineral gallery in the Museum still has the crystal species laid out in an order dictated by their chemistry. The very word “mineral” tends to conjure up a picture of some beautiful and exotic crystal in a display case, but the bulk of minerals are ordinary components of common rocks. A lump of granite is a mass of minerals locked together in a three-dimensional jigsaw. This is an easy fact to verify while one is waiting in a queue in the bank, where polished slabs of granite seem to be invariably displayed on columns and counters. Pale pink or white feldspars speckled among quartz give the rock its dappled texture: there will be three or four mineral species on display. A mineral species has two diagnostic properties: its chemistry and its crystallography. Even if two minerals have the same chemical formula, they can have more than one name if they display more than one fundamentally different crystal form in nature; the simplest example is diamond and graphite, which are both forms of the element carbon, but could scarcely look more different. Because there is a limited list of chemical elements and they can combine with one another only in specified ways, the number of natural mineral species is far from infinite, although there is no sign that science is running out of new discoveries just yet. Many elements are rare in nature, so minerals containing them will also be rare. The appropriately named rare earth elements (with strange names like Yttrium) are very seldom found either singly or in quantity, although they have become very important in geochemistry and can almost be counted atom by atom with modern instruments. Despite their rarity, rare earth elements are useful. Yttrium is used in the high-intensity lamps of cinema projectors, for example. Some elements, like the noble gases we have already met, are so snooty that they won’t combine with anything else except under very exceptional circumstances. By contrast, a few elements—silica, aluminium, oxygen, iron, calcium, carbon, hydrogen—are so abundant that minerals combining some of them in various permutations are found practically everywhere. Silicates—compounds of common quartz—are especially fecund and various because silica molecules can join together in all manner of different ways to form sheets or nets that welcome in the other common elements. Many families of minerals, with names like pyroxenes, feldspars or amphiboles, are silicates that share a common structure. When pure and well formed, a given mineral will usually have a characteristic crystal shape, and often one we find beautiful. This crystalline perfection is a reflection in the hand specimen of the way atoms are stacked and arranged right down at the atomic level. The mineral mica, for example, breaks up into thin sheets if plucked with a fingernail, and the silicate molecules of which it is composed are also arranged in sheets. Common rock salt crystallizes into cubes, and the elements sodium and chlorine of which it is composed are also arranged cubically. The macrocosm mirrors the microcosm.

Mineral structure at the molecular level was first investigated by the great X-ray crystallographers: Sir Lawrence Bragg and his successors. The X-rays sneak in between the lattice of atoms to produce characteristic arrays of diffraction patterns related to the way the atoms are stacked. These modern investigators built upon centuries of work by early mineralogists. One could argue that science itself grew up among the alembics of the alchemists; on the bench in front of these arcane wiseacres would have been elemental sulphur crystals, or minerals with ancient names like realgar or orpiment. Some of these minerals were derived from smoking fumaroles around active volcanoes such as Mount Vesuvius, the very distillations of the bowels of the Earth. Between the seventeenth and the twentieth centuries the chemical elements were teased out of their compounds one by one. There was a metaphorical dimension to the discovery of a deeper truth about matter, which was mirrored in the geological depths from which many of the minerals originated. Mineralogy came from this ancient tradition, and the modern science gradually shed the esoteric baggage of its forebears. One of the earliest no-nonsense science
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books was Georgius Agricola’s
De rerum metallica
(1555), a practical guide to mineralogy and the arts of mining. It remained useful for several centuries. As knowledge of chemistry and the elements developed, the old furnaces of the alchemists were replaced by the blowpipes of the assayers, and then by the batteries of reagents—strong acids, solvents and poisonous cyanides—used by “wet” chemists, the men and women who use test tubes and titration to identify the composition of a mineral. Even today there is still a “wet lab” in the Natural History Museum used to identify certain of the lighter elements. But most of the routine work of assessing chemical composition of the majority of minerals is now entrusted to high-tech equipment: electron probe microanalysis and ion probes can work on tiny quantities of material, even a sample only five microns across, that is, five-thousandths of a millimetre, plucking out and sorting its atoms to an accuracy of picagrams (that is, a million millionth of a gram). There is something almost mystical about these kinds of figures, something that should inspire in the ordinary person a feeling not unlike the awe felt by an initiate wandering into the alchemist’s lair. But as the figures are derived from machines, faced with dials and plasma screens that are familiar from a hundred films featuring the scientist at work, somehow the achievement of such accuracy can be taken on the nod. It is remarkable how the remarkable has become unremarked.

New minerals are still being discovered regularly, and part of the job of the Mineralogy Department is to describe them chemically and crystallographically—and only then to provide a new name. Names have to be approved, and there is a special commission of distinguished mineralogists to make sure that something claimed as new really
is
new. The International Mineralogical Association has a Commission on New Minerals, Nomenclature and Classification to vet the validity of new discoveries. A couple of dozen species might be approved in any normal month—nothing to impress a beetle enthusiast, of course, but still proving that there is much to discover within the Earth. Chris Stanley tells me that most of the new minerals he has described and named are not very exciting to look at, often no more than a dusting of tiny crystals. It is no wonder they were undetected by earlier mineralogists. He and his late colleague Alan Criddle have named nearly a hundred new mineral species over their careers. It is only thanks to the delicacy of the new technology that they can be characterized so accurately.

Occasionally, Chris gets a surprise. He showed me part of a borehole core from Serbia, something substantial enough to toss from hand to hand. The borehole had been put down through a thickness of volcanic rocks. This particular piece of core consisted largely of a milky-coloured material which proved to be a completely new mineral. It contained a high proportion of the lightest metallic element of them all, lithium, which makes it a most surprising find. In 2007 it attracted press attention because its chemical formula matched that of Green Kryptonite, the only substance to which Superman was vulnerable. It will be called Jadarite, after the place of its discovery. It must be published with details of its chemical formula, crystal structure and atomic proportions before it can be considered valid. As for naming, this geographic formality is common among new minerals; a site where a mineral species has been discovered will have “-ite” tacked on to the end of it to give the mineral name—not very imaginative, perhaps, but easy to follow. Quite frequently, a mineral will be named after a distinguished scientist, as in Zinnwaldite (after Dr. Zinnwald),
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so this is not unlike celebrating a botanist in a plant species name. Several hundred new species of minerals have been named in the Mineralogy Department over the last decade. More confusing is the fact that rock types are very often-ites as well, ranging from andesites to tholeiites, and sometimes these are named after localities, too (like Chassignite above). Such rock types are mostly collections of minerals en masse. Their definitions are much laxer than those of minerals, so there are several varieties of andesite, but they are nonetheless part of the common language of geologists, just as the names of species help communication between biologists. Nomenclature is important.

The hand specimen of the mineral Jadarite, recently named: chemically it is sodium lithium boron silicate hydroxide; it achieved unusual prominence in the media because of its resemblance to “green kryptonite”—the only substance known to weaken Superman.

Rock is the real stuff. This is proved by the voyage to the Moon: such an expedition must be validated by the collection of rock samples. All that trouble to acquire something that looks so ordinary—but you cannot argue with it, because it is solid as a rock. I recall the excitement when Moon rock appeared in the Museum in the 1970s—here was evidence you could really believe. We all looked at the small tube containing the sample with respect. It is no coincidence that Jesus’ most reliable disciple was called Peter, “the rock” on which the Church was built. The Natural History Museum keeps historical collections of rocks. Early expeditions risked nearly as much to bring back these unglamorous lumps as did the first explorers on the Moon; they, too, collected hard and most incontrovertible testimony to their boldness. Part of the Mineralogy Department is located in the basement and has been labelled “Miner Alley.” One side of the corridor has high glass cases which include splendid crystal specimens and old optical instruments, all burnished brass and elaborate screws used to raise and lower their universal stages. On the other side there is a long rank of old-fashioned cabinets containing rocks—historically significant rocks numbered in sequence and purchased with the privations or even death of forgotten field staff. Here is the sad booty of Captain Scott’s Antarctic expedition. The oldest collection is probably that made by Sir William Hamilton, envoy to Naples and cuckolded husband of Nelson’s Lady Hamilton—and also a pioneer archaeologist and writer of the magnificent
Campi Phlegraei
celebrating the wonders of the Bay of Naples. Here, too, is preserved the geological collection of the Matthew Flinders expedition to Australia in 1801, probably the first rocks ever brought back from that continent. These rock types can easily be re-collected again today, but then they were the first blobs on a geological map. Now I guess that these drawers are mostly opened by historians rather than by geologists. No doubt if Moon travel ever became routine the first Moon rocks would become historical curios in their turn. The Vesuvian rocks of the Monticelli collection are the exception: they are still consulted, because of the precision of the times, dates and places of their acquisition by their careful collector. Geologists who want to know how magma evolves during a volcanic eruption have here a unique database of past crises.

Even the way that rocks are studied—the science of petrology—has changed repeatedly. When I was a student, the chief tool for studying rocks was the prepared thin section (like the one on colour plate 13). The rock was trimmed of a thin slice, which was mounted on a slide, and then ground still thinner until its component minerals could be studied under the microscope by shining a directed beam through them. The mosaic of minerals so revealed had a chequered beauty, like a brilliantly coloured abstract painting, especially when viewed under conditions of polarized light. We were taught to identify minerals by their optical properties, as our teachers had themselves been taught by the Cambridge legends of the light microscope, Professors Tilley and Harker. There was a certain satisfaction in learning these mineralogical skills, and some intellectual satisfaction to be had in linking our identifications with the chemistry of the rocks themselves. Ph.D. students cut literally hundreds of thin sections to get their data on composition of magmas, or the temperature and pressure conditions to which a particular gneiss had been subjected when it was deep within the Earth’s crust. A modest number of thin sections continue to be sliced today for petrological microscope study. Opaque minerals, such as those in meteorite “irons,” are still studied from highly polished surfaces. But the sophistication and convenience of the analytical machines have transformed the study of rocks, so that thin sections now play a lesser part in most research. Old timers will grumble, as old timers will, that the youngsters “wouldn’t know an adamellite if it hit them in the face.” But scientific instruments change, just as research priorities change—though I cannot see an old electron probe making as attractive an exhibit as those beautiful essays in tooled brass and hand-ground lenses that line the walls of “Miner Alley.”