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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.

Elbaite

in Pollucite - #37761
Locality
Mount Mica quarry, Paris, Oxford Co., Maine, United States 
Formula
Na(Al1.5Li1.5)Al6(BO3)3Si6O18(OH)4 
Availability
Sold
Size
3.5 x 2.5 x 1.5 cm - Miniature 
Tagged
pegmatite mineral  

The late Art Smith acquired this specimen from David Seaman in the 1980's (see prov. tab). It is a nice representative specimen from this zoned pegmatite of "rubellite" elbaite tourmaline in colorless Pollucite. Mount Mica pegmatite can be classified as a poorly zoned Lithium-Cesium-Tantalum pegmatite. It was one of Maine's first gem mines and is a serial producer of gem quality tourmaline.


Elbaite

Formula
Na(Al1.5Li1.5)Al6(BO3)3Si6O18(OH)4 
Crystal System
Trigonal 
Crystal Habit
Striated, Prismatic 
Cleavage
Indistinct, None, None 
Luster
Vitreous (Glassy) 
Color
blue, colorless, green, yellow, white 
Streak
white 
Class
Trigonal - Ditrigonal Pyramidal 
Fracture
Sub Conchoidal 
Hardness
7.5 
Collection
Art Smith Collection
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Ernstite

#BM40522
Locality
Linopolis, Divino das Larajeiras, Minas Gerais, Brazil 
Formula
(Mn2+,Fe3+)AlPO4(OH,O)2 
Availability
Sold
Size
5.5 x 4 x 4 cm - Sm Cabinet 
Tagged
phosphate , pegmatite mineral  

Large crystals of Ernstite replacement of Eosphorite. The green is possibly Mitridatite. Ernstite usually occurs in just pegmatites, but it also occurs at the Big Fish phosphorite deposits in the Yukon of Canada.


Ernstite

Collection
McConlogue Collection
On Dakota Matrix
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Ernstite

#40571
Locality
White Cap mine, Pennington Co., South Dakota, United States 
Formula
(Mn2+,Fe3+)AlPO4(OH,O)2 
Availability
Sold
Size
5 x 3.5 x 2.5 cm - Miniature 
Tagged
phosphate , pegmatite mineral  

The White Cap mine is a zoned pegmatite in the Keystone district. A boulder there produced several secondary phosphates of which this is one of them. Ernstite had never been found in the Black Hills prior to this. It was verified by Andy Roberts, The amber brown spray on this specimen is about 1mm and there are a few smaller. These crystals show good terminations, are translucent, and look much like Eosphorite, however they are not bladed but rather prismatic.


Ernstite

On Dakota Matrix
Previously Sold Ernstite
On Dakota Matrix
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Fersmanite

with Aegerine & Albite - #PD40472
Locality
Eveslogchorr Mt, Khibiny Massif, Kola Peninsula, Russia 
Formula
Ca4(Na,Ca)4(Ti,Nb)4(Si2O7)2O8F3 
Availability
Sold
Size
6 x 4 x 3.5 cm - Sm Cabinet 
Tagged
pegmatite mineral  
Special Info
Type Locality 

Fersmanite was discovered in 1922 at Eveslogchorr Mt, but thought to be just titanite however, it was later found to contain Niobium. It was described in 1926. The mineral was named after the famous Russian mineralogist Aleksandr Evgen'evich Fersman (1883-1945), one of the founders of modern geochemistry.  Fersmanite occurs in this specimen as translucent crystal grains to 8mm with Aegerine, Albite, and possibly Pectolite. It was originally found in aegerine-nepheline-microcline pegmatite vein with lamprophyllite, pectolite, and apatite. The nepheline syenite pegmatites differ from granitic pegmatites in that they are alkali and quartz deficient (silica-undersaturated).


Fersmanite

Formula
Ca4(Na,Ca)4(Ti,Nb)4(Si2O7)2O8F3 
Crystal System
Monoclinic 
Crystal Habit
Pseudo Tetragonal 
Cleavage
None, None, None 
Luster
Vitreous (Glassy) 
Color
golden yellow, resin brown, light brown, dark brown 
Streak
brownish white 
Class
Monoclinic - Prismatic 
Fracture
Uneven 
Hardness
5.5 
Collection
Phillips Collection
Special Info
Type Locality

Fluorapatite

in Albite - #PD40488
Locality
Strickland pegmatite, Middlesex Co., Connecticut, United States 
Formula
Ca5(PO4)3
Availability
Sold
Size
9 x 8 x 8 cm - Sm Cabinet 
Tagged
phosphate , pegmatite mineral  

A chunk of cleavelandite with bluish Fluorapatite.


Fluorapatite

Formula
Ca5(PO4)3
Crystal System
Hexagonal 
Crystal Habit
Massive - Granular, Euhedral Crystals 
Cleavage
Indistinct, None, None 
Luster
Vitreous - Resinous 
Color
blue, brown, colorless, violet, green 
Streak
white 
Class
Hexagonal - Dipyramidal 
Fracture
Brittle - Conchoidal 
Hardness
Collection
Phillips Collection

Fluorapatite

#DH40572
Locality
King Lithia mine, Pennington Co., South Dakota, United States 
Formula
Ca5(PO4)3
Availability
Sold
Size
7 x 4 x 4 cm - Sm Cabinet 
Tagged
phosphate , pegmatite mineral  

The King Lithia mine is one of the few pegmatites in the Black Hills where good crystals of Fluorapatite can be found. They are typically prismatic, lustrous and purple. This specimen has a cluster of purple crystals as wells as several smaller in cleavelandite Albite matrix.


Fluorapatite

Formula
Ca5(PO4)3
Crystal System
Hexagonal 
Crystal Habit
Massive - Granular, Euhedral Crystals 
Cleavage
Indistinct, None, None 
Luster
Vitreous - Resinous 
Color
blue, brown, colorless, violet, green 
Streak
white 
Class
Hexagonal - Dipyramidal 
Fracture
Brittle - Conchoidal 
Hardness
Collection
Hess Collection

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