Club	Location	Distance
New Haven Mineral Club	New Haven, Connecticut	3km
Lapidary and Mineral Society of Central Connecticut	Meriden, Connecticut	24km
Bristol Gem & Mineral Club	Bristol, Connecticut	37km
Danbury Mineralogical Society	Danbury, Connecticut	45km

Mindat Locality ID:

47302

Long-form identifier:

mindat:1:2:47302:3

GUID (UUID V4):

Mill Rock is a diabase intrusive forming a 3/4-mile long, E-W trending ridge cross-cutting the Triassic New Haven Arkose. Mineralization was reported in a small quarry at the west end. Dana (1877) reports on the initial find:

"[Garnets] occur on the line of contact between the trap and the adjoining sandstone, and probably owe their origin to the metamorphic action of the heat of the erupted rock. They are found best in seams and little cavities in the trap, where they are implanted as isolated crystals upon an earlier deposit of quartz crystals. Occasional garnets of indistinct crystalline form but presumably of similar origin occur on the surfaces of the sandstone adjoining; scales of hematite produced by metamorphic action are common on the same surfaces."

Two specimens can be viewed via the Yale Peabody Museum on-line collection at the links below.

Dana (1891) reported veins of prenite and laumontite, with "traces of copper ore" associated with the prehnite vein in a small quarry at the west end of the ridge. Eaton (1927) went there later and managed to find more laumontite.

Dana (1891) mentions another smaller quarry at the eastern corner of Mill Rock Road (coordinates). Eaton (1927) called it the Powder House Quarry and mentions finding prehnite and minor copper mineralization there.

Select Mineral List Type

Standard Detailed Gallery Strunz Chemical Elements

Mineral List

9 valid minerals.

Detailed Mineral List:

✪ Andradite

Formula: Ca₃Fe³⁺₂(SiO₄)₃

Habit: modified rhombic dodecahedrons

Colour: wine yellow

Description: "The Mill Rock garnets have a wine-yellow color, and a brilliant luster. The material available was much too scanty to admit of any chemical examination, but in view of their similarity of form and color, they may safely be referred to the variety topazolite." (Dana, 1877). They are a couple of mm across or less, associated with quartz.

References:

Dana, Edward S. (1877) On the occurrence of Garnets with the Trap of New Haven, Connecticut. American Journal of Science: s3-14(81): 215-218.

✪ Andradite var. Topazolite

Formula: Ca₃Fe³⁺₂(SiO₄)₃

Habit: modified rhombic dodecahedrons

Colour: wine yellow

References:

Dana, Edward S. (1877) On the occurrence of Garnets with the Trap of New Haven, Connecticut. American Journal of Science: s3-14(81): 215-218.

ⓘ Bornite

Formula: Cu₅FeS₄

References:

Eaton, Frederick S. (1927): Mineral Localities of Connecticut. Rocks & Minerals, vol. 2, no. 4, pp. 141-2.

ⓘ Cuprite

Formula: Cu₂O

References:

Eaton, Frederick S. (1927): Mineral Localities of Connecticut. Rocks & Minerals, vol. 2, no. 4, pp. 141-2.

ⓘ Epidote

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

References:

Longwell & Dana, 1932. Walks & Rides in Central CT & MA, p.228.

ⓘ Hematite

Formula: Fe₂O₃

Habit: scales

Description: In the sandstone near the contact with the diabase.

References:

Longwell & Dana, 1932. Walks & Rides in Central CT & MA, p.228.

Dana, Edward S. (1877): On the occurrence of Garnets with the Trap of New Haven, Connecticut. American Journal of Science Series 3, Volume 14, page 215.

ⓘ Hematite var. Specularite

Formula: Fe₂O₃

Description: In the baked arkose below the contact with the diabase.

References:

Longwell & Dana, 1932. Walks & Rides in Central CT & MA, p.228.

Eaton, Frederick S. (1927): Mineral Localities of Connecticut. Rocks & Minerals, vol. 2, no. 4, pp. 141-2.

ⓘ Laumontite

Formula: CaAl₂Si₄O₁₂ · 4H₂O

Colour: flesh

Description: Massive vein material in vertical fractures.

References:

Eaton, Frederick S. (1927): Mineral Localities of Connecticut. Rocks & Minerals, vol. 2, no. 4, pp. 141-2.

ⓘ Malachite

Formula: Cu₂(CO₃)(OH)₂

References:

Eaton, Frederick S. (1927): Mineral Localities of Connecticut. Rocks & Minerals, vol. 2, no. 4, pp. 141-2.

ⓘ Prehnite

Formula: Ca₂Al₂Si₃O₁₀(OH)₂

Habit: botryoidal aggregates

References:

Eaton, Frederick S. (1927): Mineral Localities of Connecticut. Rocks & Minerals, vol. 2, no. 4, pp. 141-2.

ⓘ Quartz

Formula: SiO₂

Colour: white

Description: Druses lining cavities associated with andradite.

References:

Dana, Edward S. (1877) On the occurrence of Garnets with the Trap of New Haven, Connecticut. American Journal of Science: s3-14(81): 215-218.

Gallery:

List of minerals arranged by Strunz 10th Edition classification

Group 2 - Sulphides and Sulfosalts
ⓘ	Bornite	2.BA.15	Cu₅FeS₄
Group 4 - Oxides and Hydroxides
ⓘ	Cuprite	4.AA.10	Cu₂O
ⓘ	Hematite	4.CB.05	Fe₂O₃
ⓘ	var. Specularite	4.CB.05	Fe₂O₃
ⓘ	Quartz	4.DA.05	SiO₂
Group 5 - Nitrates and Carbonates
ⓘ	Malachite	5.BA.10	Cu₂(CO₃)(OH)₂
Group 9 - Silicates
ⓘ	Andradite	9.AD.25	Ca₃Fe³⁺₂(SiO₄)₃
ⓘ	var. Topazolite	9.AD.25	Ca₃Fe³⁺₂(SiO₄)₃
ⓘ	Epidote	9.BG.05a	(CaCa)(AlAlFe³⁺)O[Si₂O₇][SiO₄](OH)
ⓘ	Prehnite	9.DP.20	Ca₂Al₂Si₃O₁₀(OH)₂
ⓘ	Laumontite	9.GB.10	CaAl₂Si₄O₁₂ · 4H₂O

List of minerals for each chemical element

H	Hydrogen
H	ⓘ Epidote	(CaCa)(AlAlFe³⁺)O[Si₂O₇][SiO₄](OH)
H	ⓘ Laumontite	CaAl₂Si₄O₁₂ · 4H₂O
H	ⓘ Malachite	Cu₂(CO₃)(OH)₂
H	ⓘ Prehnite	Ca₂Al₂Si₃O₁₀(OH)₂
C	Carbon
C	ⓘ Malachite	Cu₂(CO₃)(OH)₂
O	Oxygen
O	ⓘ Andradite	Ca₃Fe₂³⁺(SiO₄)₃
O	ⓘ Cuprite	Cu₂O
O	ⓘ Epidote	(CaCa)(AlAlFe³⁺)O[Si₂O₇][SiO₄](OH)
O	ⓘ Hematite	Fe₂O₃
O	ⓘ Laumontite	CaAl₂Si₄O₁₂ · 4H₂O
O	ⓘ Malachite	Cu₂(CO₃)(OH)₂
O	ⓘ Prehnite	Ca₂Al₂Si₃O₁₀(OH)₂
O	ⓘ Quartz	SiO₂
O	ⓘ Hematite var. Specularite	Fe₂O₃
O	ⓘ Andradite var. Topazolite	Ca₃Fe₂³⁺(SiO₄)₃
Al	Aluminium
Al	ⓘ Epidote	(CaCa)(AlAlFe³⁺)O[Si₂O₇][SiO₄](OH)
Al	ⓘ Laumontite	CaAl₂Si₄O₁₂ · 4H₂O
Al	ⓘ Prehnite	Ca₂Al₂Si₃O₁₀(OH)₂
Si	Silicon
Si	ⓘ Andradite	Ca₃Fe₂³⁺(SiO₄)₃
Si	ⓘ Epidote	(CaCa)(AlAlFe³⁺)O[Si₂O₇][SiO₄](OH)
Si	ⓘ Laumontite	CaAl₂Si₄O₁₂ · 4H₂O
Si	ⓘ Prehnite	Ca₂Al₂Si₃O₁₀(OH)₂
Si	ⓘ Quartz	SiO₂
Si	ⓘ Andradite var. Topazolite	Ca₃Fe₂³⁺(SiO₄)₃
S	Sulfur
S	ⓘ Bornite	Cu₅FeS₄
Ca	Calcium
Ca	ⓘ Andradite	Ca₃Fe₂³⁺(SiO₄)₃
Ca	ⓘ Epidote	(CaCa)(AlAlFe³⁺)O[Si₂O₇][SiO₄](OH)
Ca	ⓘ Laumontite	CaAl₂Si₄O₁₂ · 4H₂O
Ca	ⓘ Prehnite	Ca₂Al₂Si₃O₁₀(OH)₂
Ca	ⓘ Andradite var. Topazolite	Ca₃Fe₂³⁺(SiO₄)₃
Fe	Iron
Fe	ⓘ Andradite	Ca₃Fe₂³⁺(SiO₄)₃
Fe	ⓘ Bornite	Cu₅FeS₄
Fe	ⓘ Epidote	(CaCa)(AlAlFe³⁺)O[Si₂O₇][SiO₄](OH)
Fe	ⓘ Hematite	Fe₂O₃
Fe	ⓘ Hematite var. Specularite	Fe₂O₃
Fe	ⓘ Andradite var. Topazolite	Ca₃Fe₂³⁺(SiO₄)₃
Cu	Copper
Cu	ⓘ Bornite	Cu₅FeS₄
Cu	ⓘ Cuprite	Cu₂O
Cu	ⓘ Malachite	Cu₂(CO₃)(OH)₂

Other Databases

GeoNames ID:	4838722

Other Regions, Features and Areas containing this locality

North AmericaContinent

North America PlateTectonic Plate

Ganderia DomainDomain
GranderiaPassive Margin

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References

collections.peabody.yale.edu (n.d.) https://collections.peabody.yale.edu/search/Record/YPM-MIN-053357

collections.peabody.yale.edu (n.d.) https://collections.peabody.yale.edu/search/Record/YPM-MIN-020918

Dana, Edward S. (1877) On the occurrence of Garnets with the Trap of New Haven, Connecticut. American Journal of Science: s3-14(81): 215-218.

Dana, James D. (1891) On the Four Rocks of the New Haven Area, East Rock, West Rock, Pine Rock and Mill Rock, in Illustration of the Features of Non-Volcanic Igneous Injections. With a Guide to Walks and Drives about New Haven. Tuttle, Morehouse and Taylor, New Haven: 10-15, 52.

Eaton, Frederick S. (1927) Mineral Localities of Connecticut. Rocks & Minerals: 2 (4): 141-2.

Longwell & Dana. (1932) Walks & Rides in Central Connecticut and Massachusetts: 228.

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Mill Rock, Hamden, New Haven County, Connecticut, USAiRegional Level TypesMill RockRidge HamdenTown New Haven 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 Databases

Other Regions, Features and Areas containing this locality

References

Mill Rock, Hamden, New Haven County, Connecticut, USA i
Regional Level Types
Mill Rock Ridge
Hamden Town
New Haven County County
Connecticut State
USA Country