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Amblygonite - Montebrasite with Fourmarierite

#41615

Amblygonite - Montebrasite with Fourmarierite

#41615
Availability
Sold
Size
7 x 6 x 4 cm - Sm Cabinet 
Formula
LiAlPO4F (RRUFF)
Locality
Tin Mountain mine, Custer Co., South Dakota, United States
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 

Data courtesy of Webmineral.

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