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A widespread exogenetic effect accompanying the crystallization of lithium pegmatites is the introduction of small amounts of lithium into the wall rocks. Lithium is not found in altered wall rock around pegmatites that do not contain independent lithium minerals. This metasomatic lithium is housed in a number of different minerals, especially muscovite, biotite, tourmaline, and holmquistite. Lithium-bearing hedenbergite and hornblende each have been reported from a single deposit. Likewise, lepidolite and zinnwaldite have each been reported once, but proof of their identities has not been given. Thus it may be affirmed that the major pegmatic species (spodumene, lepidolite, petalite, amblygonite, Fe-Mn-Li phosphates) are not formed exogenetically.
Mineralogically, two types of lithium metasomatism are known. (1) The lithium is restricted to combinations of muscovite, biotite (usually also contains Li, Rb, Cs) and tourmaline. This type occurs typically in micaceous schists or gneisses around zoned or structurally complex pegmatites that contain lepidolite, amblygonite, Fe-Mn-Li phosphates ± spodumene. (2) The lithium occurs chiefly in holmquistite (± a narrow Li-biotite zone closer to the pegmatite). This is developed invariably in hornblendic wall rocks around unzoned, poorly zoned (Kings Mtn. type), or zoned pegmatites that contain early-crystallized spodumene, usually as the sole lithium species, or with petalite, rarely with lepidolite.
The number of holmquistite occurrences is now known to be ten, with a new discovery at Bernic Lake.
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