A rolled earth fill dam with stone slope protection created by the U. S. Army Corps of Engineers between 1949 and 1952. Most of the subsequent lake is in Mansfield, Tolland Co., but the dam itself is in Windham. Coordinates are for the approximate mid-point of the 4.8-km-long dam. Uncertain where the stone came from, but Hope Valley Alaskite Gneiss is exposed in the state park and matches specimens found on the dam. Beryl (variety aquamarine)/fluorite/quartz occur in a 3-4 cm vein cross-cutting the gneiss.

Select Mineral List Type

Standard Detailed Gallery Strunz Chemical Elements

Mineral List

15 valid minerals.

Detailed Mineral List:

ⓘ Albite

Formula: Na(AlSi₃O₈)

References:

Former Fred Schuster collection

ⓘ 'Allanite Group'

Formula: (A1²⁺REE³⁺)(M1³⁺M2³⁺M3²⁺)O[Si₂O₇][SiO₄](OH)

References:

Weber, Marcelle H. and Earle C. Sullivan. (1995): Connecticut Mineral Locality Index. Rocks & Minerals (Connecticut Issue): 70(6): 403.

ⓘ Annite

Formula: KFe²⁺₃(AlSi₃O₁₀)(OH)₂

Habit: micaceous

Colour: black

Description: Most obvious in calcite-rich veins cutting annite gneiss (probably Tatnic Hill Formation).

References:

Eric Quinter collection

ⓘ Beryl

Formula: Be₃Al₂(Si₆O₁₈)

Habit: prismatic

Colour: aqua

Description: Subhedral crystals to 4 cm embedded in smoky quartz, albite, rosy microcline and fluorite.

References:

Weber, Marcelle H. and Earle C. Sullivan. (1995): Connecticut Mineral Locality Index. Rocks & Minerals (Connecticut Issue): 70(6): 403.

ⓘ Calcite

Formula: CaCO₃

Habit: anhedral

Colour: white

Description: Cleavable masses in veins with annite, pyrite, chlorite and rutile cutting annite gneiss (probably Tatnic Hill Formation).

References:

Eric Quinter collection

ⓘ 'Chlorite Group'

Habit: granular masses

Colour: dark green

Description: In veins with calcite, annite, pyrite, and rutile cutting annite gneiss (probably Tatnic Hill Formation).

References:

Eric Quinter collection

ⓘ Epidote

Formula: (CaCa)(AlAlFe³⁺)O[Si₂O₇][SiO₄](OH)

References:

James Bouthillier collection.

ⓘ Fluorite

Formula: CaF₂

Colour: colorless to smoky

Fluorescence: blue under long wave UV

Description: massive grains with aquamarine, usually crumble out leaving voids

References:

Weber, Marcelle H. and Earle C. Sullivan. (1995): Connecticut Mineral Locality Index. Rocks & Minerals (Connecticut Issue): 70(6): 403.

ⓘ 'Garnet Group'

Formula: X₃Z₂(SiO₄)₃

References:

James Bouthillier collection.

ⓘ Goethite

Formula: α-Fe³⁺O(OH)

References:

Former Fred Schuster collection

ⓘ 'Hornblende Root Name Group'

Formula: ◻Ca₂(Z²⁺₄Z³⁺)(AlSi₇O₂₂)(OH,F,Cl)₂

ⓘ Magnetite

Formula: Fe²⁺Fe³⁺₂O₄

References:

Weber, Marcelle H. and Earle C. Sullivan. (1995): Connecticut Mineral Locality Index. Rocks & Minerals (Connecticut Issue): 70(6): 403.

ⓘ Microcline

Formula: K(AlSi₃O₈)

Habit: massive

Colour: rosy

Description: Host mineral, with quartz, for beryl crystals.

References:

Former Don Miller collection

ⓘ Molybdenite

Formula: MoS₂

References:

James Bouthillier collection.

ⓘ Pyrite

Formula: FeS₂

Habit: cubic, pyritohedral

Description: Crude crystals to 1.5 cm in calcite/annite/chlorite/rutile veins cutting annite gneiss (probably Tatnic Hill Formation).

References:

Weber, Marcelle H. and Earle C. Sullivan. (1995): Connecticut Mineral Locality Index. Rocks & Minerals (Connecticut Issue): 70(6): 403.

ⓘ Pyrrhotite

Formula: Fe_1-xS

References:

Weber, Marcelle H. and Earle C. Sullivan. (1995): Connecticut Mineral Locality Index. Rocks & Minerals (Connecticut Issue): 70(6): 403.

ⓘ Quartz

Formula: SiO₂

Habit: massive

Colour: smoky

Description: Host mineral, with microcline, for beryl crystals.

References:

Former Don Miller collection

ⓘ Rutile

Formula: TiO₂

Habit: elongated prism

Colour: black

Description: Micro crystals embedded in calcite with granular chlorite, in veins with annite and pyrite cutting annite gneiss (probably Tatnic Hill Formation).

References:

Eric Quinter collection

ⓘ Titanite

Formula: CaTi(SiO₄)O

Habit: rectangular, tabular prisms

Colour: yellow-green

Description: Schooner (1961) states: "Golden crystals, up to a couple of inches across, and fairly thick, have been collected, by the author, at the Mansfield Hollow Dam; they accompany hornblende."

References:

Schooner, Richard. (1961): The Mineralogy of Connecticut. Fluorescent House, Branford, Connecticut.

Gallery:

Be₃Al₂(Si₆O₁₈)ⓘ Beryl

List of minerals arranged by Strunz 10th Edition classification

Group 2 - Sulphides and Sulfosalts
ⓘ	Pyrrhotite	2.CC.10	Fe_1-xS
ⓘ	Molybdenite	2.EA.30	MoS₂
ⓘ	Pyrite	2.EB.05a	FeS₂
Group 3 - Halides
ⓘ	Fluorite	3.AB.25	CaF₂
Group 4 - Oxides and Hydroxides
ⓘ	Goethite	4.00.	α-Fe³⁺O(OH)
ⓘ	Magnetite	4.BB.05	Fe²⁺Fe³⁺₂O₄
ⓘ	Quartz	4.DA.05	SiO₂
ⓘ	Rutile	4.DB.05	TiO₂
Group 5 - Nitrates and Carbonates
ⓘ	Calcite	5.AB.05	CaCO₃
Group 9 - Silicates
ⓘ	Titanite	9.AG.15	CaTi(SiO₄)O
ⓘ	Epidote	9.BG.05a	(CaCa)(AlAlFe³⁺)O[Si₂O₇][SiO₄](OH)
ⓘ	Beryl	9.CJ.05	Be₃Al₂(Si₆O₁₈)
ⓘ	Annite	9.EC.20	KFe²⁺₃(AlSi₃O₁₀)(OH)₂
ⓘ	Microcline	9.FA.30	K(AlSi₃O₈)
ⓘ	Albite	9.FA.35	Na(AlSi₃O₈)
Unclassified
ⓘ	'Chlorite Group'	-
ⓘ	'Hornblende Root Name Group'	-	◻Ca₂(Z²⁺₄Z³⁺)(AlSi₇O₂₂)(OH,F,Cl)₂
ⓘ	'Garnet Group'	-	X₃Z₂(SiO₄)₃
ⓘ	'Allanite Group'	-	(A1²⁺REE³⁺)(M1³⁺M2³⁺M3²⁺)O[Si₂O₇][SiO₄](OH)

List of minerals for each chemical element

H	Hydrogen
H	ⓘ Annite	KFe₃²⁺(AlSi₃O₁₀)(OH)₂
H	ⓘ Epidote	(CaCa)(AlAlFe³⁺)O[Si₂O₇][SiO₄](OH)
H	ⓘ Goethite	α-Fe³⁺O(OH)
H	ⓘ Hornblende Root Name Group	◻Ca₂(Z₄²⁺Z³⁺)(AlSi₇O₂₂)(OH,F,Cl)₂
H	ⓘ Allanite Group	(A1²⁺REE³⁺)(M1³⁺M2³⁺M3²⁺)O[Si₂O₇][SiO₄](OH)
Be	Beryllium
Be	ⓘ Beryl	Be₃Al₂(Si₆O₁₈)
C	Carbon
C	ⓘ Calcite	CaCO₃
O	Oxygen
O	ⓘ Albite	Na(AlSi₃O₈)
O	ⓘ Annite	KFe₃²⁺(AlSi₃O₁₀)(OH)₂
O	ⓘ Beryl	Be₃Al₂(Si₆O₁₈)
O	ⓘ Calcite	CaCO₃
O	ⓘ Epidote	(CaCa)(AlAlFe³⁺)O[Si₂O₇][SiO₄](OH)
O	ⓘ Goethite	α-Fe³⁺O(OH)
O	ⓘ Magnetite	Fe²⁺Fe₂³⁺O₄
O	ⓘ Microcline	K(AlSi₃O₈)
O	ⓘ Quartz	SiO₂
O	ⓘ Rutile	TiO₂
O	ⓘ Titanite	CaTi(SiO₄)O
O	ⓘ Hornblende Root Name Group	◻Ca₂(Z₄²⁺Z³⁺)(AlSi₇O₂₂)(OH,F,Cl)₂
O	ⓘ Garnet Group	X₃Z₂(SiO₄)₃
O	ⓘ Allanite Group	(A1²⁺REE³⁺)(M1³⁺M2³⁺M3²⁺)O[Si₂O₇][SiO₄](OH)
F	Fluorine
F	ⓘ Fluorite	CaF₂
F	ⓘ Hornblende Root Name Group	◻Ca₂(Z₄²⁺Z³⁺)(AlSi₇O₂₂)(OH,F,Cl)₂
Na	Sodium
Na	ⓘ Albite	Na(AlSi₃O₈)
Al	Aluminium
Al	ⓘ Albite	Na(AlSi₃O₈)
Al	ⓘ Annite	KFe₃²⁺(AlSi₃O₁₀)(OH)₂
Al	ⓘ Beryl	Be₃Al₂(Si₆O₁₈)
Al	ⓘ Epidote	(CaCa)(AlAlFe³⁺)O[Si₂O₇][SiO₄](OH)
Al	ⓘ Microcline	K(AlSi₃O₈)
Al	ⓘ Hornblende Root Name Group	◻Ca₂(Z₄²⁺Z³⁺)(AlSi₇O₂₂)(OH,F,Cl)₂
Si	Silicon
Si	ⓘ Albite	Na(AlSi₃O₈)
Si	ⓘ Annite	KFe₃²⁺(AlSi₃O₁₀)(OH)₂
Si	ⓘ Beryl	Be₃Al₂(Si₆O₁₈)
Si	ⓘ Epidote	(CaCa)(AlAlFe³⁺)O[Si₂O₇][SiO₄](OH)
Si	ⓘ Microcline	K(AlSi₃O₈)
Si	ⓘ Quartz	SiO₂
Si	ⓘ Titanite	CaTi(SiO₄)O
Si	ⓘ Hornblende Root Name Group	◻Ca₂(Z₄²⁺Z³⁺)(AlSi₇O₂₂)(OH,F,Cl)₂
Si	ⓘ Garnet Group	X₃Z₂(SiO₄)₃
Si	ⓘ Allanite Group	(A1²⁺REE³⁺)(M1³⁺M2³⁺M3²⁺)O[Si₂O₇][SiO₄](OH)
S	Sulfur
S	ⓘ Molybdenite	MoS₂
S	ⓘ Pyrite	FeS₂
S	ⓘ Pyrrhotite	Fe_1-xS
Cl	Chlorine
Cl	ⓘ Hornblende Root Name Group	◻Ca₂(Z₄²⁺Z³⁺)(AlSi₇O₂₂)(OH,F,Cl)₂
K	Potassium
K	ⓘ Annite	KFe₃²⁺(AlSi₃O₁₀)(OH)₂
K	ⓘ Microcline	K(AlSi₃O₈)
Ca	Calcium
Ca	ⓘ Calcite	CaCO₃
Ca	ⓘ Epidote	(CaCa)(AlAlFe³⁺)O[Si₂O₇][SiO₄](OH)
Ca	ⓘ Fluorite	CaF₂
Ca	ⓘ Titanite	CaTi(SiO₄)O
Ca	ⓘ Hornblende Root Name Group	◻Ca₂(Z₄²⁺Z³⁺)(AlSi₇O₂₂)(OH,F,Cl)₂
Ti	Titanium
Ti	ⓘ Rutile	TiO₂
Ti	ⓘ Titanite	CaTi(SiO₄)O
Fe	Iron
Fe	ⓘ Annite	KFe₃²⁺(AlSi₃O₁₀)(OH)₂
Fe	ⓘ Epidote	(CaCa)(AlAlFe³⁺)O[Si₂O₇][SiO₄](OH)
Fe	ⓘ Goethite	α-Fe³⁺O(OH)
Fe	ⓘ Magnetite	Fe²⁺Fe₂³⁺O₄
Fe	ⓘ Pyrite	FeS₂
Fe	ⓘ Pyrrhotite	Fe_1-xS
Mo	Molybdenum
Mo	ⓘ Molybdenite	MoS₂

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References

Schooner, Richard. (1961): The Mineralogy of Connecticut. Fluorescent House, Branford, Connecticut.

Weber, Marcelle H. and Earle C. Sullivan. (1995): Connecticut Mineral Locality Index. Rocks & Minerals (Connecticut Issue): 70(6): 403.

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Mansfield Hollow Dam, Windham, Windham County, Connecticut, USAiRegional Level TypesMansfield Hollow DamDam WindhamTown Windham CountyCounty ConnecticutState USACountry function showexplain() { $("#locexplain").toggle(); if (typeof movemap === "function") movemap(); }

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Mineral List

Detailed Mineral List:

Gallery:

List of minerals arranged by Strunz 10th Edition classification

List of minerals for each chemical element

Other Regions, Features and Areas containing this locality

References

Mansfield Hollow Dam, Windham, Windham County, Connecticut, USA i
Regional Level Types
Mansfield Hollow Dam Dam
Windham Town
Windham County County
Connecticut State
USA Country