Dry Storeroom No. 1

by Richard Fortey

  The earliest vent fauna yet known to science has been recovered from one of these precocious slabs of ancient ocean floor near Yaman Kasy. It is Silurian in age, about 430 million years old. The fossil tubes of vestimentiferan worms are about the dimensions of long macaroni—but transformed into a heavy, blackish metallic-looking mass by the iron pyrites engulfing them. To a seasoned palaeontologist Yaman Kasy provides the most improbable location ever for finding evidence of past life. Normally, volcanic rocks are completely devoid of any organic remains, except in very rare cases where animals have been completely overwhelmed by an ash fall, and the idea of finding fossils in solid lumps of iron pyrites would have most of us slapping our thighs and guffawing. But then, vent faunas are a unique kind of biology, and the rulebook has to be thrown away. Little and Herrington have also found large masses of fossil vent fauna in VMSs of Devonian age in the large copper workings near Magnitogorsk; these are about fifty million years younger than the Silurian occurrence. This fauna includes a large clam and a snail as well as the ranks of tubes belonging to the specialized worms. It is a disappointment to me that no trilobites have been discovered yet in any locality—I have fantasies about them occupying the specialized bacterium-grazing niche that the crustaceans occupy today.

  It is an extraordinary tribute to the opportunism of living organisms that even this strangest of habitats should have been colonized so early. There remain some controversial aspects to the interpretation of the fauna: some workers have claimed that the animals were not living as deep as they are today. And Richard Herrington and his colleagues are still putting together the story of the appearance of the Urals, which certainly involves several separate phases of island arcs being accreted to the edge of the ancient continents (arc “docking”), and may also involve major fault movements that slid chunks of ground lengthways along the mountain chain. Differences in metallic composition from one ore body to another can be explained by different origins within the vanished ocean. Richard is working on a complex story of alteration products of VMS by the actions of hot fluids that modify the chemical composition and mineralogy of ores after they are formed. It is a convoluted story, but at the end awaits a better understanding of how our Earth is put together, as well as new sources of wealth. Minerals are the end product of natural cookery in the cauldron of the Earth—and the recipe can be reshuffled several times. Who knows if some tiny crystals may yet prove to be a new species, having waited two hundred million years to receive the blessing of a name?

  There are even odder rocks under study in the Mineralogy Department. Carbonate rocks like limestones and dolomites are abundant sedimentary rocks. They form the Cretaceous white cliffs of Dover in England, and the Permian Capitan reefs of the Carlsbad Caverns National Park in the United States. Limestones are just about everywhere, not least as building stones—they flavour much of France, and impart that soft, golden glow to Bath. Many of these rocks were originally formed from chemical precipitation of carbonates from seawater, often associated with bacterial activity, or from the fossils of animals with shells made of calcite or aragonite (these are common forms of calcium carbonate). They are where a palaeontologist likes to go to work; they belong to the world of sea, life and sunlight. Imagine, then, an eruption of carbonates from a volcano. Yet this is exactly what happens when Oldoinyo Lengai, an active volcano south of Lake Natron in the eastern Rift Valley of Africa, bursts into life. The geologist Arthur Holmes described the 1917 event thus: “The volcano suddenly burst into an eruption which lasted several months and shrouded the country for miles with soda-permeated ash. With the first rains the water holes became fouled with bitter salts and many herds of cattle died through drinking from the contaminated pools. Lava that flowed down the slopes of the volcano cracked into irregular blocks looking like grey cement.” It is a weird, bleak place, where all the usual rules of rock behaviour are suspended. These volcanic rocks are known as carbonatites, and they have been studied at the Natural History Museum by several generations of scientists. Some of the earliest samples were collected by the Overseas Geological Survey early in the twentieth century and sent back to England, where Campbell Smith, who eventually became Keeper of Mineralogy, recognized that they were erupted as lavas rather than being limestones caught up in an eruption. Then an incorrigibly amiable scientist, Alan Woolley, subsequently made carbonatites his life’s work, and continues to work on them in retirement, while Frances Wall carries forward their study into the next generation.

  Geology evidently requires patience. Nowadays carbonatites are recognized all over the world, from different geological ages, some of them even in very ancient rocks dating from the Precambrian. But as more has been learned about them, the more interesting they prove to be. Frances Wall glows with magmatic enthusiasm on the subject, while Alan Woolley erupts in chortling flows of words. Some of the most curious carbonatites have proved to have diamonds in them. This tells us that they originate not from the higher levels of the crust where sedimentary limestones are normally found, but from very deep down inside the Earth—even from the mantle, where temperatures and pressures are enough to convert the dross of carbon into sparklers, albeit rather small ones. It seems that this kind of carbonatite is extruded from “tubes” punched deep through the lithosphere. Occasionally, these conduits carry up lumps of dark mantle material, displaced messengers from the depths, as happens near the Monticchio Lakes in Italy. Quite commonly, little balls, or spherulites, of graphite about a millimetre across can be separated from the samples, and these are believed to have originated from the parent magma at a temperature about 700 degrees centigrade. Frances has been pursuing carbonatites in fieldwork in the southern Naratau Mountains of Uzbekistan; this undulating area of arid nothingness at the western end of the Tien-Shan would tempt only a geologist or an ascetic seeking mortification of the flesh; or possibly someone in search of the way diamonds form in nature. Once samples had been collected, experimental work could continue back at the laboratory: if a sample of the Uzbek carbonatite rock is seeded with graphite and then the mixture is melted under great pressure, the conditions needed for diamond formation can be replicated. It turns out that diamonds precipitate out at a pressure of 7Gpa and a temperature range of 1,200–1,570 degrees centigrade. It seems that if conditions were extreme enough diamonds might be formed within the carbonatite magma itself deep within the Earth.

  Yet another bleak area yielding carbonatites embraces the boundary between Finland and Russia: the Kola Peninsula. Endless forests of dwarf conifers and glacial lakes give way to boggy permafrost, the kind of landscape that swaps freezing winter wastes for a brief episode dominated by summer mosquitoes. In this remote region carbonatites were formed in a different way from “pipes” penetrating deeply into the Earth’s innards. Instead, they formed at depth in the Earth’s crust during a phase of intrusion of a great body of hot igneous magma, one that was already particularly enriched in sodium and potassium. A kind of distillation of magma operates here. As more and more minerals are crystallized out, the remaining magma becomes progressively richer in the “leftovers”: volatile components, or elements which have particular affinity for sodium, or even awkward elements that are reluctant to fit in anywhere else. It is a process of progressive refinement, and—like the business that goes on in an oil refinery—several different products can be produced according to local circumstances. Many volatile fluids invade the country rocks, where they crystallize slowly in fissures, to form pegmatites—the source of some of the most perfect and beautiful minerals. Bathed in fluids and gases, these crystals can slowly grow to perfection, as if to please a godly gemmologist, every face perfectly sculpted, and their design naturally determined by their constituent atoms. But because these are carbonatite magmas, the pegmatites contain minerals that are found nowhere else on Earth—they have been enriched in rare elements that provide the ingredients for a host of unusual chemical compositions. The elements concerned include names such as Lanthanum and Yttrium—the rare ele
ments mentioned above. The bleak wastes of the Kola Peninsula provide an unrivalled diversity of strange species of minerals, a gem-hound’s dream. Some of them are as beautiful as rubies, though far, far more rare. Frances Wall and her colleagues have produced a catalogue of these species, a concatenation of odd names like Scherbakovite or Kovdorskite (colour plate 15), which immortalize a bunch of Russian mineralogists and place-names. When the Natural History Museum started working in the Kola, the local Russian mineralogists compiled a shopping catalogue of minerals available there: not one of these minerals was represented in the collections in London. Now we have at least a selection; everyone benefits from international collaboration. Nor are minerals containing rare earth elements of purely academic interest. These elements are of increasing importance in the electronics industry, and wise money is moving into this area, with the unfailing instinct that money always has for the coming thing.

  The public gallery displaying the minerals is unusual in the Natural History Museum in also housing the bulk of the collections. For the rest of the Museum departments the collections are so vast that only a tiny part of them is actually in the galleries. Furthermore, every gallery elsewhere in the Museum has been revamped over the last couple of decades, but the mineral display at the eastern end of the first floor has been preserved in something like its original state. The Victorian Society is delighted. It is an airy space, well lit from the generous windows, and with glass-topped cabinets running in ranks transversely across the gallery, each of which includes a fine selection of specimens. The arrangement of minerals in the cases is by natural “families” of minerals—so the sulphides will be found together, as will the native elements like gold and copper, or the oxides, and so on. It is a teaching collection in a way that no longer exists elsewhere in the building. An eager visitor might spend weeks in here learning, and would emerge at the other end as something of a mineralogist. Underneath the glass cases are ranks of polished drawers locked safely away that contain the systematic collections. Under silica, for example, there is every variety of quartz from brilliantly transparent rock crystal, through yellow citrine or delicately pink rose quartz, to amethyst or red jasper. Some specimens are perfect pointed crystals, others banded agates which somehow recall elaborate confectionery. I last saw the latter on the way to the Moroccan desert, where every bend in the road across the High Atlas comes with a small boy waving agate geodes.*21 When the curator, Alan Hart, jangled his special keys to let me in on these secrets, I noticed one of the students edging over to have a peep in the drawer. I could read his expression, at once furtive and riveted: “What! Yet more riches!” Alan showed me one mineral that could not be displayed at all to common view. Proustite has a blood-red colour that fades when exposed to light—a shy creature, indeed. It was not named after the novelist Marcel Proust, though one feels it should have been. These famous, well-formed crystals mined from Copiapo, Chile, some of which would almost cover your hand, have an unreal quality, as if they did not quite belong on this Earth at all. I suppose that since they are a compound of silver, arsenic and sulphur they must also be very poisonous. They thus combine a lethal but hidden beauty; they are of the Earth, but somehow also unearthly. Wordsworth was no friend of geologists, whom he regarded as dull enumerators of facts, but he did write a line that seems quite appropriate to gemstones: “True beauty lies in deep retreats.”

  The mineral gallery of the Natural History Museum in about 1920. The systematic arrangement of minerals is preserved today, even though most of the exhibits elsewhere in the Museum have been transformed from their early-twentieth-century state.

  Edward Heron-Allen, polymath, novelist, palaeontologist and historian of the violin

  Alan Hart then unlocked the drawer housing a special amethyst, safe from causing more trouble at last. The catalogue describes it thus (BM Register 1944, 1): “Quartz (var. Amethyst), faceted, oval (3.5 × 2.5 cm), mounted in silver ring in form of snake, one of which bears two scarabs of amethystine quartz, the other a T in silver, engraved. Locality unknown. Mrs. Mair Jones of London by presentation, January 28, 1944.” Mrs. Mair Jones was the daughter of Edward Heron-Allen, one of the great Museum benefactors until his death in 1943, whose collection of an estimated 25,000,000 specimens formed the backbone for studies of single-celled Foraminifera in the Palaeontology Department. Heron-Allen was an extraordinary polymath, a skilled violinmaker and Persian linguist as well as a world authority on “forams.” He published everything from novels (Kisses of Fate, 1888), translations (The Ruba’iyat of Omar Khayyam, 1898), poems (The Ballades of a Blasé Man, 1891), history (Selsey Bill, Historic and Prehistoric, 1911) and bibliography (De Fidiculis Bibliographia, Being an Attempt Towards a Bibliography of the Violin, 1890–94) to natural history (Barnacles in Nature and Myth, 1928), not to mention shadier material on what would now be called alternative beliefs (A Manual of Cheirosophy, 1885). One thinks of Dryden’s lines: “A man so various that he seemed to be / Not one, but all mankind’s epitome.” Mrs. Mair Jones included a letter from her father that explains all about the curse of the amethyst. Yellowed with age now, it still lies with the specimen in the locked drawer:

  To—whomsoever shall be the future possessor of the Amethyst, these lines are addressed in mourning before he, or she, shall assume the responsibility for owning it.

  This stone is trebly accursed and is stained with the blood, and the dishonour of everyone who has ever owned it. It was looted from the treasure of the Temple of the God Indra at Cawnpore during the Indian Mutiny in 1855 and brought to this country by Colonel W. Ferris of the Bengal Cavalry. From the day he possessed it he was unfortunate, and lost both health and money. His son who had it after his death, suffered the most persistent ill-fortune till I accepted the stone from him in 1890. He had given it once to a friend, but the friend shortly afterwards committed suicide and left it back to him by will. From the moment I had it, misfortunes attacked me until I had it bound round with a double headed snake that had been a finger ring of Heydon the Astrologer, looped up with zodiacal plaques and neutralized between Heydon’s Magic Tau and two amethyst scaraboei of Queen Hatasu’s period, bought from Der-el-Bahari (Thebes). It remained thus quietly until 1902, though not only I, but my wife, Professor Ross, W. H. Rider and Mrs Hadden frequently saw in my library the Hindu Yoga, who haunts the stone trying to get it back. He sits on his heels in a corner of the room, digging in the floor with his hands, as if searching for it. In 1902, under protest I gave it to a friend, who was thereupon overwhelmed with every possible disaster. On my return from Egypt in 1903 I found she had returned it to me, and after another great misfortune had fallen on me I threw it into the Regent’s Canal. Three months afterwards it was brought back to me by a Wardour St dealer who had bought it from a dredger. Then I gave it to a friend who was a singer, at her earnest wish. The next time she tried to sing her voice was dead and gone and she has never sung since. I feel that it is exerting a baleful influence over my new born daughter so I am now packing it in seven boxes and depositing it at my bankers, with directions that it is not to see the light again until I have been dead thirty three years. Whoever shall then open it, shall first read this warning, and then do as he pleases with the jewel. My advice to him or her is to cast it into the sea. I am forbidden by the Rosicrucian Oath to do this, or I would have done it long ago.

  (Signed) Edward Heron-Allen

  October, 1904

  I think we get a fair picture of the Heron-Allen style from this letter. The amethyst (see colour plate 15) is an ordinary-looking stone to have had such a “baleful” history. The curses that lie on several famous diamonds might be construed as a way of discouraging thieves, but a humble amethyst would not be worth that kind of trouble. And it really did wait thirty-three years before finding its way to a Museum drawer, which hardly suggests a hoax. I confess to experiencing a measure of nervousness when I handled the jewel, and I am sure that it was pure coincidence that my back seized up most painfully on the following day. There
have been requests to wear the amethyst at Museum parties, but Alan Hart keeps it safely out of harm’s way under lock and key. I am told that nobody has yet reported a Hindu Yoga scrabbling at the cupboard to try to retrieve the accursed amethyst and return it to Cawnpore.

  There are some jewels that are just too valuable to be placed out in the galleries. These are kept in a very large green safe in an office behind a door that opens to a special key. I had better not tell you exactly where the door is. Hidden away, of course, are diamonds. When I was shown the contents of the safe, it did produce a little thrill to hold a large cut diamond, of a size that might interest a seriously rich film star. To a mineralogist, however, an imperfect diamond may well be more interesting than a flawless piece of “ice.” Minute inclusions within the body of the diamond can reveal much about its conditions of formation deep within the Earth. Diamonds on the surface of the Earth are strangers from a strange world, hijacked upwards to Garrard’s and Fabergé. Tiny bubbles, so small as to be hardly visible under a lens, can be analysed by techniques like Raman microspectography, which uses a laser beam to excite the constituents of the bubble into revealing their spectral properties. No harm comes to the diamond. Diamonds have a simple crystal form. In the hidden collection there is a diamond octahedron the size of a cherry—the octahedron is its uncut natural shape—still emerging from its bed of yellow ground. This was an historic find from 1872 in South Africa, at the beginning of the exploitation of the diamond pipes that founded the fortunes of the De Beer family, who subsequently provided the Natural History Museum with a Director, and who still dominate the market today. Weathered yellow ground preceded the fresher blue ground as the pipes were mined ever deeper, and both are a legacy of the deep event immortalized by a profound duct that runs towards the centre of the Earth. Seventy-five per cent of diamonds were formed in an event about three billion years ago. Scientists are still arguing why this should be, but it means that the impurities in diamonds are potentially one of the best ways to learn about our planet at an early stage of development. For example, large-scale ion microprobes have investigated the sulphur isotopes in tiny flecks included in diamonds that are effectively “fossils” preserved from the early Earth. The results show that at this early stage in the Earth’s history the sulphur from the diamonds was likely to have been derived from the atmosphere. Diamonds are a mineralogist’s—and not just a girl’s—best friend.