Amblygonite

AMBLYGONITE (from the Greek words "amblys", which means "obtuse", and "gonia", which means "angle", according to the angles on the crystals and cleavage splinters * EN: amblygonite; DE: Amblygonit; FR: amblygonite; ES: ambligonita; RU: амблигонит) is the mineral of the class of phosphates, LiAl[PO4](F,OH).

There exist the continuous isomorphic series between the amblygonite proper (F>OH) and almost fluorine-free montebrasite. The intermediate members of the series are most common, for example the hebronite (ratio F:OH is 1:1). The actual content of Li2O in amblygonite is at most 9.2% (by mass). The Li part is isomorphically substituted by Na (up to 11.2% of Na2O within the natromontebrasite). It crystallizes in the triclinic crystal system. The crystal structure is of the laminate type. There are characteristical the large isolates of the irregular shape (blocks, nodules, granular aggregates) and grains. The block isolates are most typical for the montebrasite. The colour is white, yellowish, greenish. The polysynthetic twins are common. The cleavage is perfect in one direction and distinct in another one. It is often semi-transparent or translucent. The hardness is 6-6.5; it is brittle. The density is from 2900 (montebrasite) to 3100 (amblygonite) kilograms per cubic metre.

Amblygonite is the typical mineral of the rare-metallic (lithium) granitic pegmatites, it is also sometimes found within the albitized alaskites, greisens, and quartz veins together with cassiterite.

Amblygonite is the valuable lithium ore, but significant accumulations are rare, and because of this the extraction is not large. The main method of benefication is flotation; the collectors are the fatty acids and their soaps; the reverse flotation is also used. The block amblygonite is sometimes extracted from pegmatites with the help of the manual ore sorting.