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Dyke Park, Stamford, Fairfield Co., Connecticut, USAi
Regional Level Types
Dyke ParkPark
Stamford- not defined -
Fairfield Co.County
ConnecticutState
USACountry

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Key
Lock Map
Latitude & Longitude (WGS84): 41° 2' 9'' North , 73° 32' 18'' West
Latitude & Longitude (decimal): 41.03583,-73.53833
GeoHash:G#: dr79qw750
Locality type:Park
Köppen climate type:Cfa : Humid subtropical climate
Nearest Settlements:
PlacePopulationDistance
Stamford128,874 (2017)2.0km
Old Greenwich6,611 (2017)2.6km
Riverside8,416 (2017)3.3km
Cos Cob6,770 (2017)5.1km
Darien20,732 (2017)7.5km


Based on information by Lent (1967) and from field collecting, Ryerson (1972) provided a summary of this unique find:

Although the specimens collected here are presumably not native to Connecticut, this area provides a unique collecting experience. [Adjacent harbor] Dredging operations and the subsequent dumping of fill in Dyke Park and behind the Woodward [Woodland] Cemetery have yielded flint nodules and some fossils in chalk. One theory advanced for the existence of the flint and chalk in the harbor muck is that it had been used as ballast in ships in earlier days and then dumped into the harbor. The specimens are attributed to the Dover Cliffs of England. The specimens are quite attractive, and certainly a most desirable addition to one’s mineral collection. Also found here are barite and fluorescent fluorite. The dredging and dumping has been going on since late 1966; it would be difficult to assess how long this will remain a collecting area. As late as June 1967, interesting specimens were still available at this location, and may continue to be so for an indefinite length of time.


However, Ludwigson (1967) reports that the nodules actually are waste from a post-World War I era chalk plant found during sea wall construction along the west branch of the harbor on property of the former Hartford Electric Light Co. Chalk was imported from Dover, England and processed in Stamford into talcum powder (which explains the presence of talc) and fillers. The nodules were screened out and piled up (some ended up in landscaping in local homes). When the plant was dismantled, the piles were dumped as fill along the edge of the harbor.

A map by Hiller (1967) shows that the finds were along the dirt road on southern to eastern shore of the park, upstream of the dam. Also, at low tide, a deposit of slag with rare copper chloride and other secondary minerals similar to those from the sub-sea slags at Laurium, Greece, but with copper instead of lead and zinc, was exposed "not far behind the ball park". These minerals are described by Henderson (1967) "From one piece of slag about three by four inches, all the above minerals were described, and more than a hundred micro specimens obtained." He reports the slag was in a waste layer with

...bottles dating from—the twentieth century as well as old glass door knobs, keys, locks and copper and brass scrap. All this material was refuse dumped by the Yale and Towne Lock Company, which manufactured keys, locks, etc., until recently at their Stamford plant...The slag probably represents partially melted scrap material. It varies from almost pure copper or brass with siliceous glass to pure coal or coke. The best mineralization is found in pieces where there is sufficient glassy material to form almost water-tight vesicles but sufficient copper to supply material to make up the minerals.


The flint nodules have the white, gray to black interior and white external chalk coating typical of the Dover material. Barite, galena and fluorite, which is highly fluorescent like English material, were also abundant elsewhere in England, so the association makes some sense, but why these are present, too, is odd.

Regions containing this locality

North America PlateTectonic Plate

Select Mineral List Type

Standard Detailed Strunz Dana Chemical Elements

Mineral List


13 valid minerals.

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!

Select Rock List Type

Alphabetical List Tree Diagram

Detailed Mineral List:

Aragonite ?
Formula: CaCO3
Habit: micro needles, acicular
Colour: white
Reference: Henderson, William, A., Jr. (1967), A Copper Analog of Laurium, Greece. Rocks & Minerals: 42(5): 273-276.
Atacamite
Formula: Cu2(OH)3Cl
Habit: micro radiating clusters, aggregates, druses
Colour: deep green, sky blue
Description: Henderson (1967) reports: deep green crystals of quite variable habit up to 0.5 mm in size. The terminal planes of single crystals were generally bright, while faces in the prism zone were rounded and striated (Fig. 3). It also occurred as radiating groups and in irregular aggregates, sometimes with a single larger crystal perched on top. Druses of atacamite on vesicles were common. It was most frequently found close to or on cuprite, but occasionally appeared to be on malachite. Identification was based on its solubility in dilute hydrochloric and nitric acids, a positive test for halogen, and negative tests for carbonate and sulfate. The atacamite showed parallel extinction and weak birefringence, the two together ruling our malachite, antlerite and brochantite. The mineral was distinguished from paratacamite by its crystal form. On occasion, crystals corresponding to atacamite were found but with a sky blue color. These may well be pseudomorphs of rosasite after atacamite.
Reference: Henderson, William, A., Jr. (1967), A Copper Analog of Laurium, Greece. Rocks & Minerals: 42(5): 273-276.
Azurite
Formula: Cu3(CO3)2(OH)2
Habit: micro tabular
Colour: blue
Description: two small groups of deep blue, very tiny platy crystals associated with malachite. The crystals were flat tablets with a vitreous luster.
Reference: Henderson, William, A., Jr. (1967), A Copper Analog of Laurium, Greece. Rocks & Minerals: 42(5): 273-276.
Baryte
Formula: BaSO4
Description: "dead ringers for English material"
Reference: Ryerson (1972): Rock Hound's Guide to Conn.; Henderson, William, A., Jr. (1967), A Copper Analog of Laurium, Greece. Rocks & Minerals: 42(5): 273-276.
Copper
Formula: Cu
Habit: micro arborescent, octahedral
Description: Henderson (1967) reports: occurs both massive and in crystals. The massive material is in irregular masses up to an inch or two in length or as small beads formed on cooling of molten material. The larger masses are invariably coated with ocher copper minerals, and usually are associated with coal or coke. Crystals are found in vesicles in slag. Up to 1.0 mm in length, the crystals are highly distorted and usually arborescent. A few specimens appeared to be octahedral in habit. Many crystals are covered with cuprite crystals, and a few pseudo-morphs of cuprite after copper occur.
Reference: Henderson, William, A., Jr. (1967), A Copper Analog of Laurium, Greece. Rocks & Minerals: 42(5): 273-276.
Cuprite
Formula: Cu2O
Habit: micro cubic, octahedral, modified by dodecahedron
Colour: deep red
Description: Henderson (1967) reports: as large masses and as crystals. Crystallized material showed the cube and/or octahedron; the dodecahedron was less commonly found, and then only as modifying faces. The deep red crystals were up to 0.5 mm in length, and occurred singly or in groups, usually on massive cuprite. Besides the equant variety, cuprite was also found as acicular crystals of chalcotrichite.
Reference: Henderson, William, A., Jr. (1967), A Copper Analog of Laurium, Greece. Rocks & Minerals: 42(5): 273-276.
Cuprite var: Chalcotrichite
Formula: Cu2O
Habit: acicular
Reference: Henderson, William, A., Jr. (1967), A Copper Analog of Laurium, Greece. Rocks & Minerals: 42(5): 273-276.
Fluorite
Formula: CaF2
Fluorescence: blue-white
Description: Masses, with strong blue-white fluorescence. "dead ringers for English material"
Reference: Ryerson (1972): Rock Hound's Guide to Conn.; Henderson, William, A., Jr. (1967), A Copper Analog of Laurium, Greece. Rocks & Minerals: 42(5): 273-276.
Galena
Formula: PbS
Description: "dead ringers for English material"
Reference: Henderson, William, A., Jr. (1967), A Copper Analog of Laurium, Greece. Rocks & Minerals: 42(5): 273-276.
Malachite
Formula: Cu2(CO3)(OH)2
Habit: needle druses
Colour: light green
Description: small, light green, velvety needles in druses
Reference: Henderson, William, A., Jr. (1967), A Copper Analog of Laurium, Greece. Rocks & Minerals: 42(5): 273-276.
Nantokite
Formula: CuCl
Habit: micro tetrahedra, etched to skeletal or in parallel groups
Colour: colorless to white
Description: Henderson (1967) reports: colorless translucent to white opaque 0.5 mm tetrahedra with and on cuprite and atacamite. Some of the crystals showed triangular etch pits on the tetrahedron faces (Fig. 1) and many were skeletal (Fig. 2) or occurred in parallel growth. Identification was made as follows. Very few white tetrahedral minerals are known, and of these, only nantokite CuCl and marshite CuI were likely to form from copper in the presence of sea water. Both these minerals are optically isotropic, and the above material was found to be so. In addition, the index of refraction was found to be about 1.93. Nantokite has an index of 1.930 while marshite has an index of 2.346. As a matter of fact, the index of refraction is alone sufficient to identify this mineral as nantokite since only a handful of minerals have indices as high as 1.9, and the above are the only tetrahedral minerals in the group. Many of the nantokite crystals were altered in part or entirely to a lime green mineral, and a few to a sulfur yellow material. It is interesting to note that nantokite has been reported to alter in air to the green mineral paratacamite.
Reference: Henderson, William, A., Jr. (1967), A Copper Analog of Laurium, Greece. Rocks & Minerals: 42(5): 273-276.
Paratacamite ?
Formula: Cu3(Cu,Zn)(OH)6Cl2
Colour: lime green
Description: Many of the nantokite crystals were altered in part or entirely to a lime green mineral, which may be paratacamite.
Reference: Henderson, William, A., Jr. (1967), A Copper Analog of Laurium, Greece. Rocks & Minerals: 42(5): 273-276.
Rosasite
Formula: (Cu,Zn)2(CO3)(OH)2
Habit: micro duses to radiating acicular aggregates
Colour: pale blue
Description: Henderson (1967) reports: found in several habits. Druses of very small, pale blue, velvety crystals were common; on occasion, the larger crystals of acicular habit formed radiating aggregates. A few single crystals were noted: these formed tapering prisms with wedge shape terminations. An occasional arborescent group of crystals was noted (Fig. 4). The rosasite tended to be further from copper and cuprite than either the nantokite or atacamite and often occurred in the seams of half-consumed coke. The material was identified as rosasite by its color, crystal form and positive test for carbonate and negative test for sulfate. Its optical properties were those of rosasite. It was distinguished from the high-zinc end member of the series, aurichalcite, by its color, aurichalcite tend¬ing toward green.
Reference: Henderson, William, A., Jr. (1967), A Copper Analog of Laurium, Greece. Rocks & Minerals: 42(5): 273-276.
Talc
Formula: Mg3Si4O10(OH)2
Reference: Henderson, William, A., Jr. (1967), A Copper Analog of Laurium, Greece. Rocks & Minerals: 42(5): 273-276.

List of minerals arranged by Strunz 10th Edition classification

Group 1 - Elements
Copper1.AA.05Cu
Group 2 - Sulphides and Sulfosalts
Galena2.CD.10PbS
Group 3 - Halides
Atacamite3.DA.10aCu2(OH)3Cl
Fluorite3.AB.25CaF2
Nantokite3.AA.05CuCl
Paratacamite ?3.DA.10cCu3(Cu,Zn)(OH)6Cl2
Group 4 - Oxides and Hydroxides
Cuprite4.AA.10Cu2O
var: Chalcotrichite4.AA.10Cu2O
Group 5 - Nitrates and Carbonates
Aragonite ?5.AB.15CaCO3
Azurite5.BA.05Cu3(CO3)2(OH)2
Malachite5.BA.10Cu2(CO3)(OH)2
Rosasite5.BA.10(Cu,Zn)2(CO3)(OH)2
Group 7 - Sulphates, Chromates, Molybdates and Tungstates
Baryte7.AD.35BaSO4
Group 9 - Silicates
Talc9.EC.05Mg3Si4O10(OH)2

List of minerals arranged by Dana 8th Edition classification

Group 1 - NATIVE ELEMENTS AND ALLOYS
Metals, other than the Platinum Group
Copper1.1.1.3Cu
Group 2 - SULFIDES
AmXp, with m:p = 1:1
Galena2.8.1.1PbS
Group 4 - SIMPLE OXIDES
A2X
Cuprite4.1.1.1Cu2O
Group 9 - NORMAL HALIDES
AX
Nantokite9.1.7.1CuCl
AX2
Fluorite9.2.1.1CaF2
Group 10 - OXYHALIDES AND HYDROXYHALIDES
A2(O,OH)3Xq
Atacamite10.1.1.1Cu2(OH)3Cl
Paratacamite ?10.1.2.1Cu3(Cu,Zn)(OH)6Cl2
Group 16a - ANHYDROUS CARBONATES CONTAINING HYDROXYL OR HALOGEN
Azurite16a.2.1.1Cu3(CO3)2(OH)2
Malachite16a.3.1.1Cu2(CO3)(OH)2
Rosasite16a.3.1.2(Cu,Zn)2(CO3)(OH)2
Group 28 - ANHYDROUS ACID AND NORMAL SULFATES
AXO4
Baryte28.3.1.1BaSO4
Group 71 - PHYLLOSILICATES Sheets of Six-Membered Rings
Sheets of 6-membered rings with 2:1 layers
Talc71.2.1.3Mg3Si4O10(OH)2
Unclassified Minerals, Mixtures, etc.
Aragonite ?-CaCO3
Cuprite
var: Chalcotrichite
-Cu2O

List of minerals for each chemical element

HHydrogen
H TalcMg3Si4O10(OH)2
H AtacamiteCu2(OH)3Cl
H Rosasite(Cu,Zn)2(CO3)(OH)2
H MalachiteCu2(CO3)(OH)2
H AzuriteCu3(CO3)2(OH)2
H ParatacamiteCu3(Cu,Zn)(OH)6Cl2
CCarbon
C Rosasite(Cu,Zn)2(CO3)(OH)2
C MalachiteCu2(CO3)(OH)2
C AzuriteCu3(CO3)2(OH)2
C AragoniteCaCO3
OOxygen
O BaryteBaSO4
O TalcMg3Si4O10(OH)2
O CupriteCu2O
O AtacamiteCu2(OH)3Cl
O Cuprite (var: Chalcotrichite)Cu2O
O Rosasite(Cu,Zn)2(CO3)(OH)2
O MalachiteCu2(CO3)(OH)2
O AzuriteCu3(CO3)2(OH)2
O ParatacamiteCu3(Cu,Zn)(OH)6Cl2
O AragoniteCaCO3
FFluorine
F FluoriteCaF2
MgMagnesium
Mg TalcMg3Si4O10(OH)2
SiSilicon
Si TalcMg3Si4O10(OH)2
SSulfur
S BaryteBaSO4
S GalenaPbS
ClChlorine
Cl NantokiteCuCl
Cl AtacamiteCu2(OH)3Cl
Cl ParatacamiteCu3(Cu,Zn)(OH)6Cl2
CaCalcium
Ca FluoriteCaF2
Ca AragoniteCaCO3
CuCopper
Cu CopperCu
Cu CupriteCu2O
Cu NantokiteCuCl
Cu AtacamiteCu2(OH)3Cl
Cu Cuprite (var: Chalcotrichite)Cu2O
Cu Rosasite(Cu,Zn)2(CO3)(OH)2
Cu MalachiteCu2(CO3)(OH)2
Cu AzuriteCu3(CO3)2(OH)2
Cu ParatacamiteCu3(Cu,Zn)(OH)6Cl2
ZnZinc
Zn Rosasite(Cu,Zn)2(CO3)(OH)2
Zn ParatacamiteCu3(Cu,Zn)(OH)6Cl2
BaBarium
Ba BaryteBaSO4
PbLead
Pb GalenaPbS

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org

Ordovician - Neoproterozoic
443.8 - 1000 Ma



ID: 3190671
Precambrian-Phanerozoic sedimentary rocks

Age: Neoproterozoic to Ordovician (443.8 - 1000 Ma)

Lithology: Mudstone-carbonate-sandstone-conglomerate

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

Middle Ordovician
458.4 - 470 Ma



ID: 2875397
Pumpkin Ground Member [of Harrison (Prospect) Gneiss]

Age: Middle Ordovician (458.4 - 470 Ma)

Stratigraphic Name: Harrison Gneiss

Description: Medium- to light-gray, medium- to coarse-grained, well-layered and foliated gneiss, composed of oligoclase, microcline, quartz, and biotite; some layers have numerous microcline megacrysts 1 to 5 cm across; others have hornblende. Minor layers of garnetiferous schist and gneiss. Pumpkin Ground and Beardsley Members of Harrison Gneiss, formerly considered conformable metavolcanic members, are here recognized as juxtaposed metaplutonic units and are renamed the Beardsley and Pumpkin Ground orthogneisses. Isotopic dating yields ages of 428+/-2 Ma (Early Silurian) for the Pumpkin Ground and 446+/-2 Ma (Late Ordovician) for the Beardsley, accepted by authors as crystallization ages. Pumpkin Ground intrudes the Trap Falls Formation. The Harrison Gneiss as described by Rodgers (1985) has no stratigraphic significance and cannot be correlated regionally (Sevigny and Hanson, 1993).

Comments: Part of Central Lowlands; Iapetus (Oceanic) Terrane - Connecticut Valley Synclinorium; Hartland Belt. Secondary unit description per CT007. Original map source: Connecticut Geological and Natural History Survey, DEP, in cooperation with the U.S. Geological Survey, 2000, Bedrock Geology of Connecticut, shapefile, scale 1:50,000

Lithology: Major:{gneiss}, Minor:{schist}

Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. [133]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License

References

Sort by

Year (asc) Year (desc) Author (A-Z) Author (Z-A)
Henderson, William, A., Jr. (1967), A Copper Analog of Laurium, Greece. Rocks & Minerals: 42(5): 273-276.
Hiller, John. (1967), unpublished sketch map.
Lent, Mrs. Vernon A. (1967): Flint Nodules in Stamford, Conn. Rocks & Minerals: 52(5): 338-339.
Ludwigson, George. (1967), Further Collecting of Flint Nodules at Stamford, Conn. Rocks & Minerals: 42(9): 643-644.
Ryerson, Kathleen. (1972): Rock Hound's Guide to Connecticut. Pequot Press.


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