Blog by Johan C Varekamp, Smith Curator of Mineralogy and Petrology of the Joe Webb Peoples Museum of Natural History, and Harold T Stearns Professor of Earth and Environmental Sciences, Emeritus
The Joe Webb Peoples Museum of Natural History has a significant number of minerals from the pegmatite quarries from the direct surroundings of Middletown. Connecticut has had its fair share of mineralogical “firsts”, and in some of these the mineral Columbite ((Fe, U, Th, Mg), (Ta, Nb)2 O6) plays a major role.
We will begin with John Winthrop the Younger (1606-1676), son of the leader of the Pilgrims/ Puritans who landed in Plymouth, the first Governor of Connecticut and an avid amateur rock collector. On November 4, 1631, English-born John Winthrop Jr. arrived on the shores of the Massachusetts Bay Colony, where his father was governor. Four years later, he received a commission to found a colony in Connecticut, which eventually became the Saybrook colony. Eleven years later, he founded New London, where he operated a gristmill that became the first monopoly granted in New England. Active in Connecticut politics, Winthrop served as the Connecticut Colony’s governor in 1657 and then again from 1659 until his death in 1676. Winthrop acquired a charter that united the Connecticut and New Haven colonies, and became a commissioner of the United Colonies of New England.
John Winthrop the Younger
As mineral collector, Winthrop found an unknown mineral that he named Columbite (after Columbus), because it was discovered in the New World. It is not clear exactly where Winmthrop found the mineral, but probably he found it somewhere close to Middletown.
He sent a piece of it to England for further study, where it remained without attention for many decades. The specimen was investigated in 1801 by Charles Hatchett (1765-1847), an English mineralogist and analytical chemist. He proclaimed that it was an oxide of an unknown element, which he named Columbium.
Charles Hatchett
The well – known English mineralogist William Hyde Wollaston (1766-1828) compared the mineral Columbite with other minerals (Tantalum-oxides) in 1809, and determined that the element Columbium probably was the same as the element Tantalum, although he actually found the element Niobium. Several decades later the elements Niobium and Tantalum were properly separated and each given its own name.
William Hyde Wollaston
Tantalum is insoluble in water as well as in strong acids, a property that gave the element its name after the Greek mythological character Tantalus, who according to mythology suffered from an ‘unquenchable thirst while standing in water’. The very similar element Niobium was then named after Tantalus’ daughter, Niobe. In the USA, Niobium is still called by some metallurgists and trade organizations Columbium, reflecting a fondness for the explorer.
Tantalus and Niobe
Columbite played an important role in the discovery of radiometric dating in earth sciences, and the first scientific estimates of the age of the Earth. Ernest Rutherford (1871-1937) discovered the basics of radioactivity at Cambridge University (UK) in 1906, and hypothesized that alpha particles (4He) ultimately would end up as He gas trapped in minerals that contained the parent nuclides U or Th.
Ernest Rutherford
Rutherford spent a sabbatical year at Yale University and heard about the U-Th-rich pegmatite rocks of the Portland CT area. He collected several Columbite specimen because it had struck him that – if we know the decay constant of a parent nuclide-, the amount of daughter nuclide would be a measure of the time elapsed since the mineral formed, i.e., the age of the mineral could be determined in actual years!.
Small crystal of Columbite in pegmatitic rock
He tried to measure the amount of He in these minerals, but discovered soon that not much He was there – either the rocks were very young, or the Helium, a gas, had escaped. We now know that He will escape from most minerals fairly rapidly because of its small size and noble gas unreactive properties, but the thought to carry out what we now call ‘radiometric dating’ by looking for “daughter” nuclides was correct.
U-238 decays spontaneously to Th-234 by emitting an alpha particle (He-4) and then follows a long chain of decay reactions that either emit an electron (beta particle) or another alpha particle. The ultimate final product is an isotope of lead (Pb) with weight Pb-206. Modern radiometric dating of minerals is done by comparing the amount of lead (Pb-206) with the remaining mass of U-238, knowing the rate of decay of the latter.
During the early days of radiometric dating it was Wilbur Foye of Wesleyan University who made the mineral samarskite from a location close to Glastonbury available to scientists at Harvard University, and from there the US Geological Survey and National Research Council’s Committee on the Measurement of Geologic Time. You can see samarskite in the Joe Webb Peoples Museum!
Further Reading:
- The Annals of Philosophy, 1824, Baldwin, Craddock and Joy, London UK
- John Torry, MD – An account of the Columbite from Haddam, CT. Article IX. This story refers to the piece of Columbite sent to England by John Winthrop
Interesting story: Rediscovery of the Elements: Columbium and Tantalum