This page is currently not sponsored. Click here to sponsor this page.
|Location is approximate, based on center of defined region.|
|Latitude & Longitude (WGS84):||41° North , 72° West (est.)|
Connecticut is politically divided into 8 counties - Fairfield, Hartford, Litchfield, Middlesex, New Haven, New London, Tolland, and Windham. Below the county level, the entire state is divided into 169 incorporated towns and cities, there is no unincorporated land. Typically within the boundaries of an incorporated town or city is a population center with the same name as the incorporated one, such as the town and village of East Haddam. There are also other named population centers within incorporated towns/cities that are sometimes more populated than the village with the incorporated town name, such as Falls Village in the town of Canaan, or Willimantic in the town of Windham. A few of these have established boundaries. Villages and other geographic places within an incorporated town/city typically serve as a more precise reference to a mineral locality. But in some cases there is a village with the same name as a different incorporated town. For example, the village of Canaan is in the incorporated town of North Canaan not the incorporated town of Canaan. Both of these towns include many mineral localities that if just referred to as Canaan would cause confusion.
All Connecticut localities listed in mindat.org should include:
- the name(s) of the locality
- (optional) the closest city or village or other place name (if relevant or different from the incorporated town/city) (USGS maps are a good reference)
- the name of the incorporated town/city (1 of 169)
- the county name
Connecticut has a long and complex geologic history that resulted in the presence of many types of sedimentary, igneous, metamorphic and hydrothermal rocks. There are three primary bedrock geologic regions that are part of the continental scale Appalachian Orogen:
1) Metamorphic and igneous rocks of the Western highlands.
2) Sedimentary and igneous rocks of the Central Lowlands (the Hartford Mesozoic Basin of the Newark Terrane).
3) Metamorphic and igneous rocks of the Eastern Highlands.
Within the Western Highlands the metamorphic rocks occur in three major tectonic terranes:
1) Mesoproterozoic massifs (mostly ortho and paragneisses, migmatites and amphibolites) with Neoproterozoic and Cambro-Ordovician quartzite, gneiss, schist and marble shelf sequences (Laurentian continental margin deposits), including the goethite iron ore deposits formed from metamorphosed lateritic soil. These are exposed in westernmost Connecticut and in the core of the Waterbury Dome.
2) Allochthonous Taconian (Hoosic, Manhattan and Canaan Mountain) schist and amphibolite - (Neoproterozoic and Cambrian continental slope deposits), exposed also in westernmost Connecticut.
3) Allochthonous Connecticut Valley Synclinorium and Milford-Orange Terranes (oceanic terranes consisting mostly of Cambrian to Silurian schist and granofels, and intruded by gneissic syntectonic plutons). Parts of these terranes are unconformably capped by Devonian/early Silurian The Straits Schist and Wepawaug Schist. This belt lies in the eastern and southern parts of the Western Highlands.
The Mesoproterozoic massifs underwent metamorphism during the Ottowan phase (approx. 1.05 Ga) of the Grenville Orogeny. These rocks, their Neoproterozoic to Ordovician cover, and the terranes to their east also were deformed by the Taconian and Acadian Orogenies.
Within the Western highlands there are also a few large post-tectonic plutons such as the very late Devonian Nonewaug Granite (and associated pegmatites) and Permian Pinewood Adamellite; numerous small Devonian pegmatites; and the Mesozoic Pomperaug Basin with similar sedimentary and igneous rocks as the much larger Mesozoic Hartford Basin.
The Mesozoic Hartford Basin, part of the Newark Terrane of rift basins formed during the Triassic-Jurassic breakup of Pangaea, underlies the Central Lowlands of Connecticut. It is a continental graben filled with 8-10 km of clastics - arkosic conglomerates, sandstones and mudstones with minor carbonate and petroleum-rich lacustrian shales - three basalt lava flows (including the much-quarried Jurassic Holyoke Basalt), and numerous diabase plutons (principally the Jurassic West Rock Diabase) that also extent into the adjacent highlands.
Within the Eastern Highlands the metamorphic rocks occur in six major tectonic terranes:
1) The Bronson Hill Anticlinorium, which consists of metamorphosed felsic plutons and volcanics of an Ordovician island arc. Part of this terrane is unconformably capped by Devonian/Silurian Bolton Group meta-sediments. This terrane underlies the western part of the Eastern Highlands.
2, 3) Allochthonous Merrimack and Central Maine Terranes (oceanic terranes consisting mostly of Ordovician to Devonian schist, siliceous and calc-silicate gneiss and granofels, and intruded by gneissic syntectonic plutons). These terranes are exposed in the central part of the eastern highlands.
4) Putnam-Nashoba island arc terrane consisting mostly of Ordovician orthogneisses and exposed in far eastern Connecticut and in the Willimantic Dome.
5, 6) Avalon and Gander (Stony Creek, Clinton and Lyme Domes) continental terranes consisting of Neoproterozoic gray ortho and paragneisses, quartzite, meta-granites and alaskite. The Gander Lyme Dome also includes Permian alaskite gneiss. These terranes are intruded by numerous small, post-tectonic plutons of Permian Westerly (or Narragansett Pier) granite and pegmatite. These terranes crop out along the southeastern and eastern edges of the state, and in the Willimantic Dome.
Numerous small to large very early Permian pegmatites intrude the Eastern Highlands terranes, particularly in the area east of Middletown known as the Middletown Pegmatite District.
Ductile faulting on a continental scale has greatly affected the metamorphic and igneous rocks of the Western and Eastern Highlands. Barrovian metamorphism extends from low grade (Chlorite Zone) to high grade (Sillimanite Zone), there is very little contact metamorphism (mostly around the Litchfield Norite) though there is retrograde metamorphism in many areas. Despite the extensive tectonic history, there are only a few remnants of lower oceanic igneous crust; serpentinized fragments of these are found mainly in the Satan's Kingdom area and Orange-Milford Belt.
Brittle faulting associated with the Triassic-Jurassic breakup of Pangaea affected all of Connecticut. Numerous, regional faults are mapped in the Eastern and Western Highlands and, of course, within, bordering and cross-cutting the Hartford and Pomperaug Mesozoic Basins, which formed during this time. Intense brittle faulting is particularly well exposed in the New Britain-Newington area where faults are present every few meters. Many faults and even fractures are mineralized due to hydrothermal activity, the most prominent example being the Lantern Hill quartz lode in North Stonington.
Although late Cretaceous and Tertiary transgressive sediments of the Coastal Plains of eastern North America did cover part of Connecticut, erosion has removed them. Pleistocene glaciation affected the state and deposited extensive till, deltaic sands and gravels, and lacustrian silts and clays.
Due to its long and complex geologic history, Connecticut boasts a large variety of mineral forming environments and thus a long list of mineral species. The presence of these deposits so close to major colleges and universities such as Yale, Harvard, Wesleyan, Amherst, and University of Connecticut provided specimens for study by early luminaries such as Archibald Bruce, Benjamin Silliman, Edward Dana, James Dana, George Brush, Wilbur Foye, and Charles Shepard and more recently David London. Mineral specimens from Connecticut are in the museum collections at Greenwich, Middletown, New Haven, and Kent, Connecticut; plus Cambridge and Amherst, Massachusetts; New York City; Washington, DC and beyond. It also created and continues to inspire a plethora of amateur collectors, mostly as hobbyists but also many who have made major contributions (through publications and collections) to the knowledge of the state's mines and minerals, such as Ronald Januzzi, Richard Schooner, Neal Yedlin, Charles and Marcelle Weber, Bill Shelton, John (Jack) Pawloski, Bruce Jarnot, John Hiller, Earle Sullivan, Ed Force, Bob Jones and many others.
The minerals of Connecticut can best be generally categorized by their host rock types and environments listed below.
Igneous Rock Minerals:
- Rock forming minerals in large plutons - albite, microcline/orthoclase, quartz, biotite series, muscovite, dark amphiboles, dark pyroxenes.
- Accessory minerals in large plutons - almandine, fluorapatite, titanite, zircon, rutile, allanite, monazite, schorl, pyrite.
- Rock forming minerals in basalt and diabase - anorthite, augite, pigeonite, olivine.
- Pegmatite minerals - albite (including cleavelandite), microcline, quartz, muscovite, annite, almandine, tourmalines, beryl, fluorapatite, columbite-tantalite, samarskite, uraninite (and secondaries), monazite, zircon, montebrasite, lepidolite, spodumene (and alterations), lithiophilite-triphyllite (and alterations), microlite, cookeite, topaz, opal-AN, pollucite, calcite, fluorite, sulfides, numerous other secondary and rare minerals.
Metamorphic Rock Minerals:
- Rock forming minerals in siliceous schist, gneiss, and amphibolite - albite, quartz, muscovite, biotite series, chlorite series, microcline, dark amphiboles, dark pyroxenes.
- Accessory minerals in siliceous schist, gneiss, and amphibolite - chlorite group, almandine, kyanite, sillimanite, andalusite, ilmenite, fluorapatite, staurolite, cordierite, graphite, rutile, goethite, schorl, titanite, corundum, magnetite, monazite, epidote/clinozoisite, scheelite, ferberite, sulfides.
- Rock forming minerals in marble and calc-silicate rocks - calcite, dolomite, diopside, tremolite, grossular, scapolite series, albite, phlogopite.
- Accessory minerals in marble and calc-silicate rocks - dravite-uvite, pyrite, pyrrhotite, chalcopyrite, graphite, norbergite-chondrodite, titanite, spinel/magnetite, fluorapatite, corundum, quartz, chlorite series, talc, serpentine group, wollastonite, vesuvianite, epidote/clinozoisite/zoisite, microcline, axinite, forsterite, danburite.
- Minerals in serpentinites - serpentine (antigorite, lizardite, chrysotile), talc, pyrophyllite, chlorite series, calcite, tremolite, diopside, epidote/clinozoisite, magnetite, chromite, sulfides (including secondaries).
Sedimentary Rock Minerals:
Mostly clastics consisting of fragments of quartz, feldspars and other rock types, typically cemented by albite with a small amount of hematite, chlorites, and zeolites. The bituminous lacustrian shales include pyrite and nodules of magnesite and there are rare tufa deposits composed of calcite.
- Minerals in gas vesicles in basalt and diabase - calcite, quartz/chalcedony/agate, datolite, prehnite, pectolite, apophyllite, pumpellyite, julgoldite, babingtonite, adularia, gypsum, anhydrite, celestine, goethite, hematite, sulfides, zeolites (stilbite, heulandite, natrolite, analcime, laumontite, gmelinite, chabazite, mordenite).
- Minerals in faults and fractures - quartz, calcite, dolomite, fluorite, barite, aragonite, siderite, sulfides (pyrite, chalcopyrite, galena, arsenopyrite, chalcocite, bornite) and secondaries, topaz, muscovite, prehnite, pectolite, goethite, hematite, zeolites.
Mining and Quarrying:
All of the above rock types and mineral deposits have been exploited by thousands of open quarries, underground mines, and prospects, studied by geologists and mineralogists, and combed over by collectors. Although Native Americans are known to have worked quartz, talc and serpentinite deposits, the arrival of Europeans and Africans beginning in the early 17th century saw greatly increasing demand for geologic resources.
Besides rock quarrying all over the state for construction purposes, marble deposits were worked for quicklime, particularly in the marble belt in the western part of the Western Highlands. This resource is still in great demand for a variety of purposes and was also mined during WWII for dolomite (magnesium) for aircraft production and the Manhattan Project. Marble quarries are still active in Canaan and North Canaan.
"Granite", mostly actually metamorphosed plutons or meta-volcanic gneisses but also including true Westerly (or Narragansett Pier) granite, was in great demand for construction of expanding towns and cities, and for fortifications starting in the early 19th century, until largely replaced by concrete in the early 20th century. Granite quarrying still takes place in Stony Creek (Branford) and Roxbury.
To produce all that concrete, many quarries worked the diabase and basalt in both the Hartford and Pomperaug Basins for crushed stone. Others work massive gneissic rock in the highlands. Several very large quarries are still active in the Holyoke Basalt, particularly in Southbury/Woodbury, North Branford, Wallingford/Durham, Plainville, Meriden and East Granby. These quarries represent the major mining taking place in Connecticut today. The basalt quarries, and various construction sites that blasted open this rock, sometimes opened up fantastically mineralized gas vesicles and fractures.
"Brownstone", primarily an aeolian arkosic sandstone found in the Jurassic Portland Formation of the Hartford Basin, was heavily quarried for building stone until the early 20th century, particularly at Portland and Manchester. Minor brownstone quarrying took place in Portland from the early 1990s until 2012.
Quarrying and mining for minerals concentrated on three major resources: iron from goethite and siderite; feldspar and mica from pegmatites; and baryte, quartz, and metal ores from hydrothermal veins. The majority of this activity was economically successful, except most of the mining of metal ores from hydrothermal veins. The tungsten mine in Trumbull worked accessory scheelite and ferberite in an amphibolite, but was also not successful. Nor was the cobalt-nickel mining near Great Hill in East Hampton that, like Trumbull, worked a stratigraphic deposit rather than a hydrothermal vein. Pentlandite, chalcopyrite and pyrrhotite grains in the Litchfield Norite is another non-hydrothermal metal deposit that saw failed attempts at profitable mining.
The goethite iron ores mostly originated as lateritic soil formed on an unconformity between the Stockbridge Marble and Walloomsac Schist that was preserved and later metamorphosed. This stratigraphic horizon crops out in a belt largely in Salisbury where it was mined for iron in several places from the early 18th century until 1923. Known for its toughness, Salisbury iron was in great demand for cannon, chains, anchors, and railroad wheels. The Kent mine worked geothite formed in the stratigraphically lower Cambrian Dalton Formation. Here, and at a location in Sharon where it was mined, part of the Dalton was weathered to kaolinite. Another 19th century iron mine operated on Mine Hill in Roxbury exploiting the siderite vein there, which is the largest in North America.
Microcline, muscovite and other minerals were quarried and mined from the numerous pegmatites from about 1825 until 1990. There are hundreds of pegmatite quarries, mostly in the Middletown District in the Eastern Highlands, but also scattered around the Western Highlands such as at Bethel, Ridgefield, Branchville, New Milford, and Woodbury. A burst of pegmatite mining activity took place during and after WWII when sheet mica was in great demand, and for uranium and beryllium for nuclear weapons and power. A by-product of this activity was the production of a plethora of rare and gem minerals that were used for scientific and lapidary purposes and that are still sought after by collectors. Connecticut pegmatites host 9 of the state's 15 type locality minerals or varieties as well as the first known columbite crystal. Some of the first radiometric dating of minerals used uraninite and samarskite from Branchville and Glastonbury. The Roebling quarry, Gillette quarry and Strickland pegmatite were major gem producers, particularly for colored tourmalines and beryl. Most pegmatite quarries closed after the federal subsidies for beryl and mica ended in the 1950s because the high grading of ore was largely done manually. But The Feldspar Corp. operated the state’s largest pegmatite quarries in the White Rock area of Middletown (plus the Hale and Gotta-Wannerstrom quarries in Portland) from about 1960 to 1990 using efficient floatation technology to separate the minerals from vast quantities of crushed ore.
Although not a pegmatite quarry, the quarry for the reservoir dam at East Morris worked an outlier of the Devonian Nonewaug granite and intersected numerous, large miarolitic cavities in pegmatitic phases of the granite. The cavities produced great smoky quartz and microcline crystals with albite similar in quality and size to those from granite plutons in northern New Hampshire.
Finally, the hydrothermal veins so plentiful from the Triassic-Jurassic rifting of Pangaea were exploited for a variety of minerals, primarily quartz at the giant lode at Lantern Hill and other places. Many smaller faults, particularly those cross-cutting quartzite in the highlands, are brecciated with open spaces lined with fantastic quartz crystals, such as at West Stafford, Haddam, Moosup, and Avon. Amethyst occurs at the Canton Lead Mine in Canton. The hydrothermal veins were also worked mainly for copper and baryte during the 19th century. Baryte was successfully mined in Cheshire and copper mining was moderately successful at the Simsbury Mine (the first chartered copper mine in North America) in what is now East Granby, and at the Bristol Copper Mine, famous for its fantastic chalcocite and bornite crystals. There are many small holes and shafts dug by prospectors in search of silver, lead, copper, cobalt, nickel, and the elusive gold, none of which really panned out but now provide places for mineral collectors to ply their trade.
Coordinates are at the intersection of Interstates 91 and 691, state Routes 15 and 66, and East Main Street in Meriden very near the geographic center of the state.
References covering the state, or significant regions of it, are listed below.
Mineral ListMineral list contains entries from the region specified including sub-localities
311 valid minerals. 13 (TL) - type locality of valid minerals. 1 (FRL) - first recorded locality of unapproved mineral/variety/etc.
Rock Types Recorded
Note: this is a very new system on mindat.org and data is currently VERY limited. Please bear with us while we work towards adding this information!
Rock list contains entries from the region specified including sub-localities
Select Rock List TypeAlphabetical List Tree Diagram
Entries shown in red are rocks recorded for this region.