A tale of two columbites
A trip through the maze of nomenclature
Black minerals don’t get much respect – or at least, not the kind of ga-ga affection flashy, gemmy, red, green, blue minerals do. But for me these are pretty cool black minerals.
Columbite is really a series, a solid solution extending smoothly from iron-niobium oxide, iron niobate, FeNb2O6, to manganese-niobium oxide, MnNb2O6. Why is it called columbite? Because the original name of the element with Atomic Number 41 was columbium, given to honor Christopher Columbus by English chemist Charles Hatchett when he isolated the element in 1801 in ores from America. You’ll see some histories that say the name is more directly for the United States, personified as Columbia (there’s a long complex history of the use of “Columbia” as a poetic personification of the United States, if you are interested).
The element tantalum (Atomic No. 73) was discovered in 1802, and by 1809, chemists thought tantalum and columbium were identical, and columbium was discredited. In 1846, another chemist, Heinrich Rose, identified two additional new elements in a tantalum oxide (tantalite) sample, which he named for the children of the Greek god Tantalus: niobium (for Niobe) and pelopium (for Pelops). Pelopium was later proven to be a mixture of tantalum and niobium, so it was discarded as a name. Niobium was shown to be identical with the 1801 discovery, columbium, and was NOT the same as tantalum, as columbium had been thought to be. Chemists! Can’t live with ‘em, can’t shoot ‘em.
So by the 1860s, it was pretty well accepted that we had two very similar but distinct elements here, tantalum and columbium (or niobium). Columbium had precedence as a name, but both columbium and niobium were used for many decades, mostly in the U.S. and in Europe, respectively. Finally, in 1949 the name niobium was officially chosen over columbium. To mollify any ruffled feathers of American chemists, another controversy was settled about the same time, accepting tungsten (American usage) versus wolfram (European usage) although the symbol for tungsten remains W (Thanks, International Union of Pure and Applied Chemistry </irony-sarcasm>).
Mineral names don’t necessarily have much to do with chemical names, but when the name is for the predominant element itself, you might think they’d change a name when “columbium” no longer exists. Nope. The mineral is still columbite; there is no “niobite.” At least they didn’t change the name to niobium but keep the columbium symbol, Cb; the element’s name niobium correlates with its symbol, Nb. And I guess the other good news for the element is that we don’t have to deal with the negative aspects of Christopher Columbus.
To make things more interesting, because of those varying series, from iron to manganese in both the niobates and tantalates, pure end-members [with official names like columbite-(Fe), columbite-(Mn), tantalite-(Fe), and tantalite-(Mn)] seldom exist, and most of the natural specimens are somewhere in a four-cornered phase diagram, with iron and manganese on two opposite corners, and niobium and tantalum on the other two opposite corners. Technically, you could have four series of pure end members along the edges of the diagram, but in reality all four elements usually vary some (or a lot, from 0 to 100% of each). So in the absence of detailed chemical analysis, these things get labeled “columbite-tantalite.” If you know there’s more Fe than Mn, then it’s columbite-(Fe), but it would probably have a formula like (Fe, Mn)Nb2O6, or even more likely (Fe, Mn)(Nb,Ta)2O6.
Want it to be even more “interesting”? There’s another set of complete series that has a different crystal structure. All the members of the columbite-tantalite series are orthorhombic (three perpendicular crystal axes of unequal lengths), but there is a series with the identical chemical composition, (Fe, Mn)(Nb,Ta)2O6, that has tetragonal crystallography (two equal axes and one other of different length). The tantalum-dominant tetragonal series is called tapiolite [tapiolite-(Fe) to tapiolite-(Mn)], named in 1863 for Tapio, Finnish god of the forest. If there is a defined niobium-dominant variety that’s tetragonal, I don’t know what it is.
OK, even *I* am tired of all that nomenclatural hash.
Both of the specimens in the top photos come from pegmatites, which are late-stage deposits from molten rocks in which often enough unusual elements (lithium, boron, niobium, tantalum, and more) are concentrated, typically in big crystals. At almost 9 cm wide, the misshapen crystal at left is pretty big for columbite-tantalite, and while smaller at 3 cm, the one on the right is special for me because I collected it at the Etta Mine in the Black Hills in 1969.
The pegmatites in the Black Hills of South Dakota USA are related to the intrusion of the Harney Peak Granite about 1,715 million years ago. The granite in turn is related to the last stages of the complex collision between the much older Wyoming Craton to the west and the Superior Craton to the east, a collision called broadly the Trans-Hudson Orogeny, which probably uplifted Himalaya-like mountains in what is now western North and South Dakota.
At Petaca, New Mexico, the pegmatites are much younger than those of South Dakota, but still ancient at about 1,400 million years. North-central New Mexico 1,400 million years ago was actually a fairly quiet place tectonically, and the origin of the magmas that produced these pegmatites is unclear.
Should you care about all this? Niobium is important in making thermally stable, corrosion-resistant alloys such as those in gas and steam turbines (for electricity generation), components of solar power plants, and for other kinds of steel. You can’t make a modern cell phone, computer, or automobile without tantalum capacitors, and it is also used in camera lenses and some ceramics.
The US is 100% dependent on imports for both niobium and tantalum, largely from China, Germany, Australia, Brazil, Russia, Canada, Rwanda, and Mexico, among other sources. Tantalum from the Congo, which with Rwanda produces more than half the world’s tantalum (and which probably still comes to the US via refineries in China and elsewhere), has funded civil wars there by exploiting child and slave labor; look up “blood tantalum” for more information.
The name of the mythological figure Tantalus is from a word meaning “wretched,” a reference to his punishment for trying to trick the gods into eating his son. He was made to stand in a pool of water beneath a fruit tree with low branches, with the fruit ever eluding his grasp, and the water always receding before he could take a drink. His name is also the source of the word “tantalize.”
Another good article Richard. One minor typo though - "somewhere in a four-cornered phase diagram, with iron and **magnesium** on two opposite corners". At least you know I read it! 😆
Well I was quite excited about a tiny octahedral crystal of BLACK magnetite in some precambrian schist above Loch Lomond. It deflected my compass needle! Also my wife is keen on black 🖤 flowers...