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Phosphate Rare Minerals for the Collector

Friday, 26 August 2016 12:00 PM

Primary and Metasomatic phosphates are found mostly in pegmatites, but also occur in many sedimentary deposits. Most of these phosphates look the same. We will attempt to unlock the mystery of these unique minerals which can often contain secondary phosphate minerals. 

Amblygonite

- Montebrasite - #PD35944
Locality
Hugo mine, Keystone, Pennington Co., South Dakota, United States 
Formula
LiAlPO4
Availability
Sold
Size
5 x 4 x 3.5 cm - Miniature 
Tagged
phosphate , pegmatite mineral  

A mass of pure Amblygonite-Montebrasite.


Amblygonite

Formula
LiAlPO4
Crystal System
Triclinic 
Crystal Habit
Columnar, Euhedral Crystals, Prismatic 
Cleavage
Perfect, Good, Distinct 
Luster
Vitreous - Pearly 
Color
white, yellow, gray, bluish gray, greenish gray 
Streak
white 
Class
Triclinic - Pinacoidal 
Fracture
Uneven 
Hardness
5.5-6 
Collection
Phillips Collection

Amblygonite

- Montebrasite - #PD41612
Locality
Strickland pegmatite, Middlesex Co., Connecticut, United States 
Formula
LiAlPO4
Availability
Sold
Size
8 x 8.5 x 2 cm - Sm Cabinet 
Tagged
phosphate , pegmatite mineral  

White mass of Amblygonite-Montebrasite mined in 1956.


Amblygonite

Formula
LiAlPO4
Crystal System
Triclinic 
Crystal Habit
Columnar, Euhedral Crystals, Prismatic 
Cleavage
Perfect, Good, Distinct 
Luster
Vitreous - Pearly 
Color
white, yellow, gray, bluish gray, greenish gray 
Streak
white 
Class
Triclinic - Pinacoidal 
Fracture
Uneven 
Hardness
5.5-6 
Collection
Phillips Collection

Amblygonite

- Montebrasite with Fourmarierite - #41615
Locality
Tin Mountain mine, Custer Co., South Dakota, United States 
Formula
LiAlPO4
Availability
Sold
Size
7 x 6 x 4 cm - Sm Cabinet 
Tagged
phosphate , pegmatite mineral  

White mass of undetermined end member Amblygonite-Montebrasite. One side of this specimen shows crystal terminations. Secondary uranium minerals have always been reported within the Am-Mont from Tin Mountain. Native Bismuth often occurs with the secondary uranium minerals, but I have not seen any in this specimen. I am guessing the orange in this specimen is either Curite or Fourmarierite.

Amblygonite-Montebrasite occurs as large masses at the Tin Mountain and Tin Queen mines in the Black Hills. There are several other occurences. Typically an alteration rim of Kaolinite can help distinguish it from Microcline. Density will also help.


Amblygonite

Formula
LiAlPO4
Crystal System
Triclinic 
Crystal Habit
Columnar, Euhedral Crystals, Prismatic 
Cleavage
Perfect, Good, Distinct 
Luster
Vitreous - Pearly 
Color
white, yellow, gray, bluish gray, greenish gray 
Streak
white 
Class
Triclinic - Pinacoidal 
Fracture
Uneven 
Hardness
5.5-6 
SOLD
Arrojadite-(KFe) - PD41617
Arrojadite-(KFe) - PD41617

Arrojadite-(Kfe)

#PD41617
Locality
Nickel Plate mine, Pennington Co., South Dakota, United States 
Formula
(KNa)Fe2+(CaNa2)Fe2+13Al(PO4)11(PO3OH)(OH)2 
Availability
Sold
Size
6.5 x 6 x 5 cm - Sm Cabinet 
Tagged
phosphate , pegmatite mineral  
Special Info
Type Locality 

A dark green glassy mass of Arrojadite-(KFe). This is an old Minerals Unlimited specimen with label.

Arrojadite was first found at the Nickel Plate mine, near Keystone. It is not known to alter into secondary phosphates. Until the discovery of the phosphorite deposits in the Yukon, Arrojadite was thought to be confined to pegmatites for about 100 years. At the Big Fish River, Yukon Territory, Arrojadite forms beautiful secondary crystals in hydrothermal veins..

The nomenclature of the Arrojadite group, now 14 in number, was changed by the IMA in 2006 based upon the findings of Chopin, Oberti, and Camara in American Mineralogist (2006), pg 1260-1270. As stated in this paper: "Arrojadites are the most chemically complex of primary pegmatite phosphates, and no less than sixteen elements may play a significant role." The authors site this statement from Moore and Ito from a paper on Whiteite in Mineralogical Magazine, 42, 309-323 (1979). 


Arrojadite-(Kfe)

Formula
(KNa)Fe2+(CaNa2)Fe2+13Al(PO4)11(PO3OH)(OH)2 
Crystal System
Monoclinic 
Class
Monoclinic - Domatic 
Hardness
Collection
Phillips Collection
Special Info
Type Locality

Arrojadite-(Kfe)

with Microcline - #DS44213
Locality
Chandlers Mill quarry, Sullivan Co., New Hampshire, United States 
Formula
(KNa)Fe2+(CaNa2)Fe2+13Al(PO4)11(PO3OH)(OH)2 
Availability
Sold
Size
10 x 6 x 5 cm - Cabinet 
Tagged
phosphate , pegmatite mineral  

Granular crystalline mass of green potassium-iron Arrojadite, the most common Arrojadite found mostly in pegmatites. It is a primary phase and usually will not yield secondary phosphates. The type locality is shared between Nickel Plate pegmatite near Keystone, SD and the Serra Branca south of Pedra Lavrada and named after the Arrojado Ribeiro Lisboa a Brazilian geologist.  It forms a series with dickinsonite, which contains manganese.


Arrojadite-(Kfe)

Formula
(KNa)Fe2+(CaNa2)Fe2+13Al(PO4)11(PO3OH)(OH)2 
Crystal System
Monoclinic 
Class
Monoclinic - Domatic 
Hardness
Collection
Shultz Collection
SOLD
Arrojadite-(KFe) - DH45157
Arrojadite-(KFe) - DH45157

Arrojadite-(Kfe)

#DH45157
Locality
Nickel Plate mine, Pennington Co., South Dakota, United States 
Formula
(KNa)Fe2+(CaNa2)Fe2+13Al(PO4)11(PO3OH)(OH)2 
Availability
Sold
Size
6 x 4 x 3.5 cm - Sm Cabinet 
Tagged
phosphate , pegmatite mineral  

Solid crystalline mass of Arrojadite with dark "bottle" green color. See PD41617 for more information on Arrojadite.


Arrojadite-(Kfe)

Formula
(KNa)Fe2+(CaNa2)Fe2+13Al(PO4)11(PO3OH)(OH)2 
Crystal System
Monoclinic 
Class
Monoclinic - Domatic 
Hardness
Collection
Hess Collection

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