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Thursday, March 8, 2012

Amblygonite one of the Gemological Garbage Cans


It is easy to see how amblygonite is often mistaken for other minerals this specimen mimics milky quartz
Photo by Ra'ike


As a mineral amblygonite is classified as a fluorophosphate with a chemical formula of (Li, Na)AlPO4(F, OH) that is composed of sodium, lithium, aluminum, phosphate, fluoride and hydroxide. This is a mineral occurs in pegmatite deposits were this easily mistaken for albite or other feldspars. It is readily distinguished by its density, cleavage and flame test for lithium. Amblygonite forms a solid solution series with montebrasite that is the low fluorine member of the series.

Faceted amblygonite from Brazil.
Photo by Ra'ike


This is a mineral found in LCT type pegmatites, high-temperature tin veins and greisens where it is found with spodumene, apatite, lepidolite, tourmaline and other lithium bearing minerals. It is often been used as an ore of lithium The chief commercial sources have been the deposits in California and France where the mineral contains about 10% lithium. 

A single crystal of faceting grade amblygonite.
Photo by Rob Lavinsky


The mineral amblygonite was originally discovered in Saxony, Germany by August Breithaupt in 1817 and named by him from the Greek words amblus (blunt) and gouia (blunt) because there is an obtuse angle between its cleavages.  Later the same mineral was found at Montebras, France and Hebron, Maine. Because there are slight optical differences in amblygonite found at these differing localities they are also called montebrasite and hebronite after the localities where it has been found.  The mineral is also found in large quantities in Pala in San Diego County, California as well in the Black Hills of South Dakota.  To date the largest single crystal of amblygonite measured 7.62 x 2.44 x 1.83 meters that weighed about 102 tons.

Amblygonite variety Montebrasite
Photo by Rob Lavinsky


When its transparent amblygonite is faceted into gemstones where it is set into jewelry, however because it is prone to breakage and abrasion as well as displaying hardness problems as well as toughness it is rarely mounted into jewelry.  This stone when it is cut often finds its way into collections as unmounted stones. The principle sources of this gemstone are Brazil and the United States however other countries have also produced faceting grade amblygonite such as Australia, France, Germany, Namibia, Norway and Spain.  Most of the gem quality amblygonite crystals that have a yellowish caste are found in pegmatite cavities.

2 comments:

  1. Making gems out of this one is new to me, John. Interesting mineral!

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