Fun with Labels

Happy New Year!

For mineral collectors, labels are everything. The most important thing you can put on a label is the locality, where the specimen is from, because you can always (even if it may take expensive analysis) determine what a specimen is, but the location information can be lost forever. Location is context, history, the geological and mining story for the specimen, whether it’s a work of art or a “big ugly.” For many collectors, a specimen without a location is almost valueless.

Even so, I have the occasional habit of buying things when I know the label is wrong, just for the fun of figuring it out. Sometimes it’s the mineral, sometimes it’s the locality, and sometimes it’s both.

I got the specimen here at the gift shop of a well-known mineral museum. The printed label said “Torbernite, Zaire” and included a previous collector’s catalog number (but no name). Torbernite, a copper-uranyl phosphate, is normally a bright shade of green, with typically tabular, square crystals. I knew that, so I was essentially certain these black crystals were not torbernite. But the specimen was $5, already in a little perky thumbnail box (which itself costs close to a dollar, unless you buy lots of them), so I got it.

When I got home days later (this museum was in a different state) and looked at the crystals under the microscope, it was evident that they were not my first guess, some common pyroxene (like augite) or amphibole (like hornblende), nor really any other black mineral I was readily familiar with. Let the fun begin!

I got a reasonable estimate of its hardness, less than quartz (7) but more than a pocketknife, putting it around 5 or 6 on the Mohs Hardness Scale. It has to my eye a rather distinctive luster, shiny approaching metallic, definitely opaque. It was the crystallography that was most interesting. The prisms look tetragonal or orthorhombic, and at least one had a distinctive termination, on the low-angle side as pyramids go.

I started with minerals from Zaire (now the Democratic Republic of Congo), but it became quickly evident that if there’s anything like this from there, it’s uncommon enough to lack photos on MinDat. That doesn’t mean it’s not present, but reduces the possibility, and I started thinking the label was wrong in both its mineralogy and its location.

It took quite a while, but eventually I decided tentatively that my best guess for the black crystals was ilvaite, a calcium-iron silicate. “Tentatively” because I had never seen ilvaite in person, had barely even heard of it. But the characteristics fit, and especially it had that one nice termination which was a lot like ilvaite.

Crystal drawing of orthorhombic pyramid termination of ilvaite and a crystal in my specimen. One of the angles on mine is so gentle, the form might be a dome, but it’s typical of ilvaite. Drawing originally by Goldschmidt (1913-1926), 3-D modeled using www.smorf.nl, published by MinDat on the ilvaite page.

Some months later, my friend Chris Gammons was in search of unknown obscure minerals for a student to practice x-ray diffraction on. Analysis of a fragment of my specimen showed quite definitively that it is ilvaite!! Cool.

Now the harder question, where it is from. For all my ignorance, ilvaite isn’t especially rare, and it is found from Alaska to Australia, Argentina to Austria. Some of those occurrences are somewhat distinctive, but many are not. The only associated mineral I had to go by in my specimen was quartz – not very helpful.

I spent hours looking at all the 450+ photos of ilvaite on MinDat. Since the original location information is lost, I can never be absolutely certain of the source of this piece, but my best guess is that it’s from a famous locality, Dalnegorsk, in far eastern Russia (northeast of Vladivostok). A third of all the photos of ilvaite on MinDat are from there, and the habits are close to mine. It will always be labeled “attributed to Dalnegorsk” but I’d say I’m at least 80% sure that’s its origin, with Serifos Island, Greece, as second runner up.  

Ilvaite takes its name from Ilva, the Latin name for the island of Elba, site of Napoleon’s first exile and subsequent escape. The evolution of ilvaite’s name is long and complex. If you are interested, please see this discussion on MinDat .

USGS map, annotated by me. The boundary between the North American and Eurasian Plates in eastern Siberia is ill-defined, because the plates are nearly locked to each other there.

Dalnegorsk is a very complex (and I’d say unique) lead-zinc-boron deposit with associated tin, bismuth, cadmium, and silver, first mined on a significant scale in 1907. It is a world-class boron deposit. The host rocks are Early Cretaceous (Neocomian, about 140 million years ago) turbidites and olistostromes. Turbidites are usually bedded submarine density flows of sediment, essentially a slurry of material that flows more or less coherently down a slope (typically the continental slope at the edge of the continental shelf). Olistostromes, from the Greek olistomai, to slide, and stroma, accumulation, are basically gigantic (mappable, on the order of kilometers), chaotic submarine slumps or slides of mixed material, some individual blocks of which may be hundreds of meters across (KItanchuk and others, 1996, Geology and mineral deposits of Primorsky Krai - Excerpt: in The Taukha metallogenic belt of skarn and vein boron and lead-zinc deposits: Russian Academy of Science, Far East Geological Institute, Primorye Exploration and Mapping Expedition, Vladivostok, p. 26-28; cited by Porter GeoConsultancy Pty Ltd., online database).

Late Cretaceous (Turonian to Campanian and Maastrichtian) to Paleogene (90 to 60 million years ago) volcanic and intrusive rocks of the East Sikhote-Alin Volcanic Belt brought in the magma and hydrothermal fluids that altered the host rocks to produce ore-bearing skarns. A skarn is a rock that’s not just metamorphosed (chemicals rearranged) but also metasomatized (new chemicals introduced to form new minerals). See Simanenko, 2006, Partizansky Base-Metal Skarn Deposit, Dalnegorsk Ore District, Russia: Stages of Ore Formation, Mineral Assemblages, and Typomorphism of Fahlore: in Geology of Ore Deposits, Pleiades Publishing, v. 48, p. 290-303; cited by Porter GeoConsultancy Pty Ltd., online database.

The Sikhote-Alin Volcanic Belt is related to early stages of subduction of the Pacific Plate beneath the eastern edge of Eurasia. Island arcs, associated sediment wedges, and other materials were pushed against and amalgamated to Eurasia to form part of the continent. Ongoing subduction today is located further east, in Japan, the Kuril Islands, and Kamchatka.  

All that investigation and learning was well worth the $5, and the specimen, even as ilvaite from an unknown locality, might be worth more than that!

P.S. As far as I can tell, there’s no word for “study of labels,” as vexillology is the study of flags. You can believe I would have used it if I had found one.