amblygonite, phosphate mineral composed of lithium, sodium, and aluminum phosphate [(Li,Na)AlPO4(F,OH)], that is an ore of lithium. It occurs in lithium- and phosphate-rich granitic pegmatites, often in very large, white, translucent masses. It has been mined at Keystone, S.D., and in South Africa, Zimbabwe, and several other countries. Clear material from Hebron, Maine, has been faceted as a gemstone. For detailed physical properties, see phosphate mineral (table).
Montebrasite, a similar mineral, contains more hydroxide than fluoride ion; in nature there is a continuous chemical variation, called a solid-solution series, between montebrasite and amblygonite.