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Pegmatite Minerals

Friday, 31 October 2014 06:00 PM

Pegmatites are located all over the world and have have produced not only ore minerals but scientifically important rare mineral species. We will take a look at these minerals, mostly rare species, as well as introduce you to the many complexities of these interesting geological deposits.

Astrophyllite

#PD40487
Locality
Skutesundskjær, Barkevik, Langesundsfjorden, Larvik, Vestfold, Norway 
Formula
K2NaFe2+7Ti2(Si4O12)2O2(OH)4
Availability
Sold
Size
9 x 6 x 7 cm - Sm Cabinet 
Tagged
pegmatite mineral  

Long excellent blades to 4cm of golden brown Astrophyllite. This is an old University of Chicago piece from Paul Moore. See prov. tab.


Astrophyllite

Formula
K2NaFe2+7Ti2(Si4O12)2O2(OH)4
Crystal System
Triclinic 
Crystal Habit
Bladed, Stellate, Crystalline - Fine 
Cleavage
Perfect, None, None 
Luster
Adamantine - Pearly 
Color
brown, brownish red, bronze yellow, gold yellow 
Streak
yellowish brown 
Class
Triclinic - Pedial 
Fracture
Brittle 
Hardness
3-3.5 
Collection
Phillips Collection

Autunite

#PD34049
Locality
Mitchell Co., North Carolina, United States 
Formula
Ca(UO2)2(PO4)2·10-12H2
Availability
Sold
Size
14 x 9.5 x 2 cm - Cabinet 
Tagged
pegmatite mineral  

No specific locality on this specimen, but I am sure someone can come close. It's a large plate with good yellow crystals of Autunite to 1mm. It is probably Chalk Mountain.


Autunite

Formula
Ca(UO2)2(PO4)2·10-12H2
Crystal System
Tetragonal 
Crystal Habit
Tabular, Micaceous, Foliated 
Cleavage
Perfect, Poor, Poor 
Luster
Vitreous - Pearly 
Color
yellow, pale yellow, lemon yellow, greenish yellow, pale green 
Streak
pale yellow 
Class
Tetragonal - Ditetragonal Dipyramidal 
Fracture
Uneven 
Hardness
2-2.5 
Collection
Phillips Collection
Mineralpedia
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Barytolamprophyllite

#BM40513
Locality
Palitra pegmatite, Mt. Kedykverpakhk, Lovozero Massif, Kola Peninsula, Russia 
Formula
Na3(BaK)Ti3(Si2O7)2O2(OH)2 
Availability
Sold
Size
5 x 3.5 x 2 cm - Miniature 
Tagged
pegmatite mineral  

Orange radiating rosettes to 1cm.

Dr. Igor Pekov described this pegmatite as "dry", meaning that late stage hydrothermal activity did not develop and consequently anhydrous minerals were perfectly preserved. Like many of the Lovozero pegmatites, Palitra is  feldspathoid-bearing and highly alkali or "hyperagpaite", an environment in which typical aluminum feldspars seen in granitic pegmatites cannot form for lack of aluminum and an over abundance of sodium. A good article on Palitra can be found in the Min. Record V36, pg 397 (Sept./Oct 1995).


Barytolamprophyllite

Formula
Na3(BaK)Ti3(Si2O7)2O2(OH)2 
Crystal System
Monoclinic 
Crystal Habit
Flakes, Stellate 
Cleavage
Perfect, Good, Poor 
Luster
Vitreous (Glassy) 
Color
golden brown, dark brown 
Streak
light brown 
Class
Monoclinic - Prismatic 
Fracture
Brittle 
Hardness
2-3 
Collection
McConlogue Collection

Bavenite

#PD40505
Locality
Londonderry Lithium deposit, Western Australia, Australia 
Formula
Ca4Be2Al2Si9O26(OH)2 
Availability
Sold
Size
5 x 3.5 x 4 cm - Miniature 
Tagged
beryllium , pegmatite mineral  

Pearly thin plates radiating along cleavelandite Albite fractures.


Bavenite

Formula
Ca4Be2Al2Si9O26(OH)2 
Crystal System
Orthorhombic 
Crystal Habit
Lamellar, Massive - Lamellar, Radial 
Cleavage
Perfect, Fair, None 
Luster
Vitreous - Pearly 
Color
white, green, pink, brown 
Streak
white 
Class
Orthorhombic - Pyramidal 
Fracture
Uneven 
Hardness
5.5 
Collection
Phillips Collection
Mineralpedia
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Beryllonite

#BM40495
Locality
Telirio mine, Linopolis, Minas Gerais, Brazil 
Formula
NaBePO4 
Availability
Sold
Size
2 x 1.5 x 1 cm - Thumbnail 
Tagged
phosphate , beryllium  

A colorless naturally etched specimen. A beryllium phosphate found chiefly in pegmatites.


Beryllonite

Formula
NaBePO4 
Crystal System
Monoclinic 
Cleavage
Perfect, Good, Perfect 
Luster
Vitreous - Pearly 
Color
colorless, white, light yellow 
Streak
white 
Class
Monoclinic - Prismatic 
Fracture
Brittle - Conchoidal 
Hardness
5.5-6 
Collection
McConlogue Collection

Bikitaite

#PD40408
Locality
Foote mine, Cleveland Co., North Carolina, United States 
Formula
LiAlSi2O6·H2
Availability
Sold
Size
5 x 2 x 1.5 cm - Miniature 

This specimen is totally covered by colorless bladed crystals of Bikitaite from 1 to 3mm. It is a rare lithium silicate found exclusively in pegmatites.


Bikitaite

Formula
LiAlSi2O6·H2
Crystal System
Triclinic 
Crystal Habit
Aggregates 
Cleavage
Perfect, Good, None 
Luster
Vitreous (Glassy) 
Color
colorless, white 
Streak
white 
Class
Triclinic - Pedial 
Fracture
Conchoidal 
Hardness
Collection
Phillips Collection
Mineralpedia
View Bikitaite
On Dakota Matrix
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On Dakota Matrix
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Mindat
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