Pegmatites are rocks that boast exceptionally large, rare crystals – and Middletown, CT and surrounding towns sit atop them! Pegmatites have a main mineral composition similar to granite (quartz, feldspar, and mica), but their crystals are exceptionally large, and often are associated with rare minerals like beryl and tourmaline. We highlight remarkable pegmatite specimens and CT’s geologic history in our new exhibit. The mineral columbite was first discovered in CT pegmatites and is valuable for its tantalum. CT pegmatites were first mined in South Glastonbury around 1825 for feldspar and mica. Pegmatite mining was also established in South Glastonbury, Haddam Neck, Middletown, Haddam, New Milford, Southford, and Redding. Quartz was mined for sharp tools by the Indigenous peoples; feldspar was mined for porcelain and abrasives; and mica was mined for cosmetics and electrical insulation. Elbaite, a gem-type of tourmaline, was often mined in the Gillette Quarry in Haddam Neck by miners hired by Tiffany & Co of New York, the fine jewelry retailer!
Our center piece somewhat resembles a pegmatite, although the exotic minerals tourmaline, beryl, and columbite are missing. Its large, vibrant green amazonite (alkali feldspar, var. microcline) with grey smoky quartz crystals and smaller albite (plagioclase, var. clevelandite) crystals sit within a granitic matrix. The amazonite is chemically very different from beryl, which is common in pegmatites, but the colors can be very close! This piece may come from the Jack Rabbit Mine in Colorado, USA just west of Telluride on the Utah-Colorado boundary, or Pikes Peak, CO, two of the few places to boast such specimens. Today, even much smaller pieces of this rock are highly prized in the mineral trade!
Pegmatite exhibit on display at the Joe Webb Peoples Museum of Natural History.
Today, there is a new interest in mining for lithium and tantalum, so visit the Joe Webb Peoples museum and learn more about pegmatite mining! We are open Monday-Friday, 9am-4pm on the fourth floor of Wesleyan University’s Exley Science Center. Can’t wait to visit? Read more about CT pegmatites in our blog post HERE.