Amblygonite "eyes-chain" from Brazil.

Amblygonite is a fluorophosphate mineral, (Li,Na)AlPO4(F,OH), composed of lithium, sodium, aluminium, phosphate, fluoride and hydroxide. The mineral occurs in pegmatite deposits and is easily mistaken for albite and other feldspars. Its density, cleavage and flame test for lithium are diagnostic. Amblygonite forms a series with montebrasite, the low fluorine endmember. Geologic occurrence is in granite pegmatites, high-temperature tin veins, and greisens. Amblygonite occurs with spodumene, apatite, lepidolite, tourmaline, and other lithium-bearing minerals in pegmatite veins. It contains about 10% lithium, and has been utilized as a source of lithium. The chief commercial sources have historically been the deposits of California and France.Transparent amblygonite has been faceted and used as a gemstone. As a gemstone set into jewelry it is vulnerable to breakage and abrasion from general wear, as its hardness and toughness are poor. The main sources for gem material are Brazil and the United States. Australia, France, Germany, Namibia, Norway, and Spain have also produced gem quality amblygonite.