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Brack Gem prospect (Brack prospect), East Glastonbury, Glastonbury, Hartford Co., Connecticut, USAi
Regional Level Types
Brack Gem prospect (Brack prospect)Prospect
East Glastonbury- not defined -
Glastonbury- not defined -
Hartford Co.County
ConnecticutState
USACountry

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Key
Latitude & Longitude (WGS84):
41° 38' 60'' North , 72° 31' 0'' West
Latitude & Longitude (decimal):
Locality type:
Nearest Settlements:
PlacePopulationDistance
Terramuggus1,025 (2017)4.2km
Lake Pocotopaug3,436 (2017)5.8km
East Hampton2,691 (2017)8.3km
Glastonbury Center7,387 (2017)8.9km
Glastonbury31,876 (2017)10.3km


Decomposed lithium-rich granite pegmatite. Unlike other pegmatites in this region, this one has completely decomposed feldspar, with "nests" of pocket contents occurring loose in soft clay. According to Jarnot (1995) it produced some of the finest colored gem elbaite and gem beryl from the state.

The "quarry" is no longer evident and only dirt dumps are obvious. Barton and Goldsmith (1968) provides a description of this weathered, gem-rich pegmatite that was hand-worked by the Brack family from 1958 to 1963 but is now abandoned:

The Brack prospect....is on a 71-acre tract owned by Arthur and Walter Brack of East Hampton. It is a gravel pit in the crest of a residually weathered rare-alkali pegmatite. It was being worked on weekends by the owner in 1963. Workings consisted of an irregular oval pit 150 by 75 feet in plan and 5 to 10 feet deep.

The fresh pegmatite was not exposed but the weathered material appears to be approximately in its original attitude and appears to strike northeast and dip 20° to 25° NW. It is on the crest of a ridge beneath up to 5 feet of glacial sand and gravel. Weathered mica and feldspar have shown up in test pits for 300 feet along strike. Feldspar has weathered mostly to kaolin leaving lepidolite, muscovite, quartz, beryl, and tourmaline of many colors, and some rotted cleavelandite as gravel. Some of the finest beryl and watermelon tourmaline crystals ever found in New England have been recovered. The approximately 1,000 pounds of beryl and 250 pounds of tourmaline that have been hand-sorted included approximately 200 pounds of beryl and 25 pounds of tourmaline of faceting grade. A gin pole with a 50-foot boom and ¼-ton bucket has been used to excavate the pit. It is operated by a hand winch. Screens, hand shovels, and buckets of wash water are the only other equipment used. As near as can be determined, beryl has constituted less than 0.5 percent of the material excavated to the time of this examination.


According to Susan (Brack) Boulanger, she and her sister still own the prospect in 2012.

Select Mineral List Type

Standard Detailed Strunz Dana Chemical Elements

Mineral List


11 valid minerals.

Detailed Mineral List:

Albite
Formula: Na(AlSi3O8)
Habit: massive
Description: Mostly weathered away to clays
Reference: Van King
Albite var: Cleavelandite
Formula: Na(AlSi3O8)
Description: mostly weathered away to clays
Reference: Barton and Goldsmith (1968)
Beryl
Formula: Be3Al2(Si6O18)
Reference: Rocks & Min.: 70:379
Beryl var: Aquamarine
Formula: Be3Al2Si6O18
Colour: blue
Description: good gem material found
Reference: Rocks & Min.: 70:379 Jarnot (1995)
Beryl var: Goshenite
Formula: Be3Al2(Si6O18)
Habit: hexagonal prisms
Colour: colorless
Description: a gem quality flattened crystal 8 cm in diameter retained by Brack family.
Reference: Rocks & Min.: 70:379
Beryl var: Morganite
Formula: Be3Al2(Si6O18)
Colour: pink to peach
Reference: Rocks & Min.: 70:379
Cassiterite
Formula: SnO2
Reference: Rocks & Min.: 70:398 Jarnot (1995)
'Columbite-(Fe)-Columbite-(Mn) Series'
Reference: Jarnot (1995)
Cookeite
Formula: (Al2Li)Al2(AlSi3O10)(OH)8
Habit: botryoidal aggregates of platy crystals
Colour: pale yellow to gray
Description: associated with elbaite, lepidolite, beryl
Reference: Van King
Elbaite
Formula: Na(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3(OH)
Habit: elongated prisms
Colour: green, pink, red
Description: all elbaite crystals have a thin blue cap on the pedion termination, with "watermelon" crystals and gem nodules to 5 mm common
Reference: Rocks & Min.: 70:379; Rocks & Minerals (1995) 70:396-409; Jarnot (1995)
Kaolinite
Formula: Al2(Si2O5)(OH)4
Colour: white
Description: most of the feldspar has weathered to this clay.
Reference: Jarnot (1995)
'Lepidolite'
Habit: "ball-peen" aggregates
Colour: gray to lavender
Reference: Rocks & Min.: 70:379; Rocks & Minerals (1995) 70:396-409
Microcline
Formula: K(AlSi3O8)
Reference: Van King
'Microlite Group'
Formula: A2-mTa2X6-wZ-n
Reference: Rocks & Min.: 70:398
Muscovite
Formula: KAl2(AlSi3O10)(OH)2
Reference: Van King
Quartz
Formula: SiO2
Reference: Rocks & Minerals (1995) 70:396-409
Quartz var: Smoky Quartz
Formula: SiO2
Habit: prismatic with rhombic terminations
Colour: gray to brown
Description: associated with gem crystals
Reference: Rocks & Min.: 70:379
Spessartine
Formula: Mn2+3Al2(SiO4)3
Reference: Jarnot (1995)
Staurolite
Formula: Fe2+2Al9Si4O23(OH)
Reference: Jarnot (1995)
'Tourmaline'
Formula: A(D3)G6(Si6O18)(BO3)3X3Z
Habit: elongated prisms
Colour: red to pink
Description: typically with blue color "cap" on the pedion
Reference: Rocks & Min.: 70:379
'Tourmaline var: Rubellite'
Formula: A(D3)G6(T6O18)(BO3)3X3Z
Habit: elongated prisms
Colour: red to pink
Description: typically with blue color "cap" on the pedion
Reference: Rocks & Min.: 70:379

List of minerals arranged by Strunz 10th Edition classification

Group 4 - Oxides and Hydroxides
Cassiterite4.DB.05SnO2
'Microlite Group'4.00.A2-mTa2X6-wZ-n
Quartz4.DA.05SiO2
var: Smoky Quartz4.DA.05SiO2
Group 9 - Silicates
Albite9.FA.35Na(AlSi3O8)
var: Cleavelandite9.FA.35Na(AlSi3O8)
Beryl9.CJ.05Be3Al2(Si6O18)
var: Aquamarine9.CJ.05Be3Al2Si6O18
var: Goshenite9.CJ.05Be3Al2(Si6O18)
var: Morganite9.CJ.05Be3Al2(Si6O18)
Cookeite9.EC.55(Al2Li)Al2(AlSi3O10)(OH)8
Elbaite9.CK.05Na(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3(OH)
Kaolinite9.ED.05Al2(Si2O5)(OH)4
Microcline9.FA.30K(AlSi3O8)
Muscovite9.EC.15KAl2(AlSi3O10)(OH)2
Spessartine9.AD.25Mn2+3Al2(SiO4)3
Staurolite9.AF.30Fe2+2Al9Si4O23(OH)
Unclassified Minerals, Rocks, etc.
'Columbite-(Fe)-Columbite-(Mn) Series'-
'Lepidolite'-
'Tourmaline'-A(D3)G6(Si6O18)(BO3)3X3Z
'var: Rubellite'-A(D3)G6(T6O18)(BO3)3X3Z

List of minerals arranged by Dana 8th Edition classification

Group 4 - SIMPLE OXIDES
AX2
Cassiterite4.4.1.5SnO2
Group 8 - MULTIPLE OXIDES CONTAINING NIOBIUM,TANTALUM OR TITANIUM
A2B2O6(O,OH,F)
'Microlite Group'8.2.2.1A2-mTa2X6-wZ-n
Group 51 - NESOSILICATES Insular SiO4 Groups Only
Insular SiO4 Groups Only with cations in [6] and >[6] coordination
Spessartine51.4.3a.3Mn2+3Al2(SiO4)3
Group 52 - NESOSILICATES Insular SiO4 Groups and O,OH,F,H2O
Insular SiO4 Groups and O, OH, F, and H2O with cations in [4] and >[4] coordination
Staurolite52.2.3.1Fe2+2Al9Si4O23(OH)
Group 61 - CYCLOSILICATES Six-Membered Rings
Six-Membered Rings with [Si6O18] rings; possible (OH) and Al substitution
Beryl61.1.1.1Be3Al2(Si6O18)
Six-Membered Rings with borate groups
Elbaite61.3.1.8Na(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3(OH)
Group 71 - PHYLLOSILICATES Sheets of Six-Membered Rings
Sheets of 6-membered rings with 2:1 layers
Muscovite71.2.2a.1KAl2(AlSi3O10)(OH)2
Sheets of 6-membered rings interlayered 1:1, 2:1, and octahedra
Cookeite71.4.1.2(Al2Li)Al2(AlSi3O10)(OH)8
Group 75 - TECTOSILICATES Si Tetrahedral Frameworks
Si Tetrahedral Frameworks - SiO2 with [4] coordinated Si
Quartz75.1.3.1SiO2
Group 76 - TECTOSILICATES Al-Si Framework
Al-Si Framework with Al-Si frameworks
Albite76.1.3.1Na(AlSi3O8)
Microcline76.1.1.5K(AlSi3O8)
Unclassified Minerals, Mixtures, etc.
Albite
var: Cleavelandite
-Na(AlSi3O8)
Beryl
var: Aquamarine
-Be3Al2Si6O18
var: Goshenite-Be3Al2(Si6O18)
var: Morganite-Be3Al2(Si6O18)
'Columbite-(Fe)-Columbite-(Mn) Series'-
Kaolinite-Al2(Si2O5)(OH)4
'Lepidolite'-
Quartz
var: Smoky Quartz
-SiO2
'Tourmaline'-A(D3)G6(Si6O18)(BO3)3X3Z
'var: Rubellite'-A(D3)G6(T6O18)(BO3)3X3Z

List of minerals for each chemical element

HHydrogen
H ElbaiteNa(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3(OH)
H Cookeite(Al2Li)Al2(AlSi3O10)(OH)8
H StauroliteFe22+Al9Si4O23(OH)
H KaoliniteAl2(Si2O5)(OH)4
H MuscoviteKAl2(AlSi3O10)(OH)2
LiLithium
Li ElbaiteNa(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3(OH)
Li Cookeite(Al2Li)Al2(AlSi3O10)(OH)8
BeBeryllium
Be Beryl (var: Morganite)Be3Al2(Si6O18)
Be Beryl (var: Aquamarine)Be3Al2Si6O18
Be Beryl (var: Goshenite)Be3Al2(Si6O18)
Be BerylBe3Al2(Si6O18)
BBoron
B ElbaiteNa(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3(OH)
B Tourmaline (var: Rubellite)A(D3)G6(T6O18)(BO3)3X3Z
B TourmalineA(D3)G6(Si6O18)(BO3)3X3Z
OOxygen
O ElbaiteNa(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3(OH)
O Beryl (var: Morganite)Be3Al2(Si6O18)
O Beryl (var: Aquamarine)Be3Al2Si6O18
O Beryl (var: Goshenite)Be3Al2(Si6O18)
O Tourmaline (var: Rubellite)A(D3)G6(T6O18)(BO3)3X3Z
O TourmalineA(D3)G6(Si6O18)(BO3)3X3Z
O Quartz (var: Smoky Quartz)SiO2
O BerylBe3Al2(Si6O18)
O CassiteriteSnO2
O Cookeite(Al2Li)Al2(AlSi3O10)(OH)8
O MicroclineK(AlSi3O8)
O StauroliteFe22+Al9Si4O23(OH)
O SpessartineMn32+Al2(SiO4)3
O KaoliniteAl2(Si2O5)(OH)4
O AlbiteNa(AlSi3O8)
O MuscoviteKAl2(AlSi3O10)(OH)2
O QuartzSiO2
O Albite (var: Cleavelandite)Na(AlSi3O8)
NaSodium
Na ElbaiteNa(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3(OH)
Na AlbiteNa(AlSi3O8)
Na Albite (var: Cleavelandite)Na(AlSi3O8)
AlAluminium
Al ElbaiteNa(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3(OH)
Al Beryl (var: Morganite)Be3Al2(Si6O18)
Al Beryl (var: Aquamarine)Be3Al2Si6O18
Al Beryl (var: Goshenite)Be3Al2(Si6O18)
Al BerylBe3Al2(Si6O18)
Al Cookeite(Al2Li)Al2(AlSi3O10)(OH)8
Al MicroclineK(AlSi3O8)
Al StauroliteFe22+Al9Si4O23(OH)
Al SpessartineMn32+Al2(SiO4)3
Al KaoliniteAl2(Si2O5)(OH)4
Al AlbiteNa(AlSi3O8)
Al MuscoviteKAl2(AlSi3O10)(OH)2
Al Albite (var: Cleavelandite)Na(AlSi3O8)
SiSilicon
Si ElbaiteNa(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3(OH)
Si Beryl (var: Morganite)Be3Al2(Si6O18)
Si Beryl (var: Aquamarine)Be3Al2Si6O18
Si Beryl (var: Goshenite)Be3Al2(Si6O18)
Si TourmalineA(D3)G6(Si6O18)(BO3)3X3Z
Si Quartz (var: Smoky Quartz)SiO2
Si BerylBe3Al2(Si6O18)
Si Cookeite(Al2Li)Al2(AlSi3O10)(OH)8
Si MicroclineK(AlSi3O8)
Si StauroliteFe22+Al9Si4O23(OH)
Si SpessartineMn32+Al2(SiO4)3
Si KaoliniteAl2(Si2O5)(OH)4
Si AlbiteNa(AlSi3O8)
Si MuscoviteKAl2(AlSi3O10)(OH)2
Si QuartzSiO2
Si Albite (var: Cleavelandite)Na(AlSi3O8)
KPotassium
K MicroclineK(AlSi3O8)
K MuscoviteKAl2(AlSi3O10)(OH)2
MnManganese
Mn SpessartineMn32+Al2(SiO4)3
FeIron
Fe StauroliteFe22+Al9Si4O23(OH)
SnTin
Sn CassiteriteSnO2
TaTantalum
Ta Microlite GroupA2-mTa2X6-wZ-n

References

Sort by

Year (asc) Year (desc) Author (A-Z) Author (Z-A)
Barton, William R. and Carl E. Goldsmith. (1968): New England Beryllium Investigations. U. S. Bureau of Mines: Report of Investigations 7070.
Jarnot, Bruce. (1995): The Brack Prospect: A Decomposed Lithia Gem Pegmatite in Glastonbury, Connecticut. Rocks & Minerals: 70(2): 128.
Jarnot, Bruce. (1995): Connecticut Gems & Gem Minerals. Rocks & Minerals (Connecticut Issue): 70(6): 378-382.
Weber, Marcelle H. and Earle C. Sullivan. (1995): Connecticut Mineral Locality Index. Rocks & Minerals (Connecticut Issue): 70(6): 396-409.

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