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.
