Museum

Pegmatite Quarries

Middletown District Pegmatite Quarries

(1922 paper by W. G. Foye, Geology department, Wesleyan University)

(text by Greg McHone; see also his field trip notes)

New England pegmatites have been mined since early colonial days, and Middletown area pegmatite quarries have long been studied by Wesleyan earth scientists, such as Professor Foye. Well known pegmatite localities also occur close to Glastonbury, Connecticut.

"The last active pegmatite quarry in the region was the White Rock Pegmatite Quarry, which was worked by the Feldspar Corporation and closed in the mid-1990’s. Middletown has plans to develop the property in a new industrial zone. Abandoned pegmatite quarries line the hills on either side of the Connecticut River between Glastonbury and Middle Haddam.

Most abandoned quarries are deep, water filled, and on restricted private property. Their concentration nearby to the east and south define the "Middletown Pegmatite District," which has hundreds of abandoned quarries of all sizes. This was a big industry for most of the previous two centuries!

Pegmatite is an igneous rock ("formed by fire"). It represents the cooled mineral assemblage of a hot magma (molten rock mass) that intruded along fractures in the earth's upper crust around 250 million years ago. Pegmatite is mainly composed of three minerals: quartz, orthoclase (K-feldspar) and albite (Na-feldspar), and minor volumes of mica, garnet, tourmaline, and rare minerals.

The easiest way to recognize pegmatite is to look for a yellowish-white rock which contains randomly oriented glittering (silver) mica flakes. Pegmatites of the Middletown District were some of the first rocks in the world to be analyzed by radiometric methods to determine their absolute age, which is about 280 million years. This is much younger than the metamorphic rocks around them, which are mostly older than 440 million years.

Deacon Ralph Pelton (from Portland) appears to have been the first to quarry the feldspar, around 1782. The rock was excavated, transported and probably crushed in mills along Reservoir or Carr's brook. The feldspar was then separated by hand and shipped (via the Connecticut River) to England. Much of the coarser English porcelain made in the 19th century may contain baked feldspar from Connecticut. Pegmatite is still quarried for similar ceramic industries in North Carolina and elsewhere.

When miners started finding large "books" (several feet in diameter and several inches thick) of mica, this mineral became a major (secondary) resource. The mica flakes were used as isinglass in stove and lanterns windows. As the threat of World War II loomed, the United States Government took a great interest in Connecticut's mica quarries. At that time mica was used as insulator against heat and electric current in generators, radio's, and the sparkplugs for cars and airplanes.

Feldspar extraction, however, dominated the quarry ventures. Production grew slowly but steadily between 1880 and 1960, after which it declined. Presently the pegmatite is excavated, ground, and its minerals are separated by a foamy floatation system.

The leftover quartz grains provide an ideal beach sand and can also be used to produce glass. The mica flakes are sold mainly to coat roof shingles. The feldspar is still used to produce porcelainware (platter's, wash basins, toilet bowls, etc.). Wherever you are in the United States, you may find yourself sitting on a piece of Connecticut sooner or later.


Haddam Gem-Bearing Pegmatites

"The magmas from which pegmatites cool contain a relatively high volume of superheated gases (mostly steam), which are very acidic and highly enriched in rare elements. When this magma crystallizes slowly, it creates relatively large and pure mineral crystals. Large crystal sizes, and the occurrence of hundreds of rare mineral types, have turned pegmatite quarries into a rockhound's paradise. Museum-quality specimens are still sometimes found. The most and (perhaps) least attractive of the rare minerals are beryl and uraninite, respectively.

Tourmaline, a complex silicate with boron, lithium, and many other elements, is common in some pegmatites. Although usually black and therefore not a gemstone, tourmaline can also be found as clear red (rubellite) and green (verdelite) gem crystals, which have climbed rapidly in value in recent years. Many fine gem-quality beryls and tourmalines have been found in the area, and some students have sold them to help support their college tuitions!

Beryl (a beryllium-rich silicate) can occur as white or golden yellow, blue, and green crystals. Blue beryl is faceted into the gemstone called aquamarine, yellow beryl is called heliodor, and deep green beryl provides ... emeralds. Few emeralds have been found in the Haddam woods but beryl hunters have roamed the area since the late 18th century.

One of the early rock hounds, Hall (1838), took the steamboat from New York to Hartford (50 cents fare) and "begged" the captain to put him on shore in Haddam, "I could not pass by Haddam - a place known all over the civilized earth... for its richness and variety of its mineral productions".

He tells us, "I engaged two quarry men to work for me at the famous chrysoberyl locality, Mr. Brainard's house rests on part of it (the pegmatite), I was to pay him 5 dollars for a single blast. The quarry men set themselves with good heart to the work of boring. I retired into the cornfield, away goes the charge, fragments flew, and a mass of about one quarter of a ton was thrown completely over the (Brainard) house. A few panes of glass were fractured". The experiment proved to be a "fortunate one" as Hall was able to collect many minerals, among them semi-transparent beryl. Hall ended his account with "I have done with Haddam".

Uraninite (UO2) is an uranium oxide which is frequently found in the pegmatites. The crystals are cubic and steely to brownish black. Poorly-crystallized uraninite is often referred to as pitchblende because of its black appearance. Unfortunately there are also other black minerals in pegmatite, such as tourmaline, which make it less easy to recognize pitchblende in the white pegmatite rock.

The uranium in uraninite minerals disintegrates radioactively, and its gamma rays cause a smoky brown color in adjacent quartz crystals. The "waste" products of this process include lead, helium and ... radon. Several basements (such as that of the Brainard house) and many wells are cut/drilled into pegmatitic rock bodies with relatively high radioactivity. It is especially important to check these sites for high radon concentrations.