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Amblygonite - Montebrasite

#PD34926

Amblygonite - Montebrasite

#PD34926
Availability
Sold
Size
12 x 8 x 6 cm - Cabinet 
Formula
LiAlPO4F (RRUFF)
Locality
Dunton Gem quarry, Newry, Oxford Co., Maine, United States
Tagged
phosphate , pegmatite

This is an excellent well-formed crystal of the primary phosphate, labeled as "amblygonite." All amblygonites should be labeled as within the series of amblygonite-montebrasite. Montebrasite is the OH analogue whereas amblygonite is the F end member. Ii is doubtful that in hand specimen the two can be discerned. Moore (MR May/June 1973) states that triphylite will crystallize before amblygonite-montebrasite. Crystals are known to be very large up to a meter across in several cases. Perfect crystals are usually not the case since they are typically found as rounded nodules probably a result of metasomatic reactions with the remaining fluid in the pegmatite system so this specimen is a nice example. The outer portion of the specimen is probably altered to kaolinite. Amblygonite can sometimes be hard to tell apart from ordinary feldspars but a simple hardness test can differentiate the two. However, be careful since sometimes amblygonite will have the kaolinite rim.

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.

Collection
Phillips Collection

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