Fluor-liddicoatite

minerals

beryl

spodumene

danburite

Formula: Ca(Li2Al)Al6(Si6O18)(BO3)3(OH)3F
Cyclosilicate (ring silicate), tourmaline group, forms a series with elbaite
Specific gravity: 3.02
Hardness: 7½
Streak: Light brown, white
Colour: Light-brown, pink to red, green, blue, rarely white
Common impurities: Mn,Fe,Ti,Mg,Na,H2O
Environments:

Pegmatites

A mineral first found at the Anjanabonoina pegmatites, Ambohimanambola, Betafo, Vakinankaratra, Madagascar, was originally thought to have the formula Ca(Li,Al)3Al6(Si6O18)(BO3)3(O,OH)3(OH,F) and was named "liddicoatite". Subsequently the type material was found to have the formula Ca(Li2Al)Al6(Si6O18)(BO3)3(OH)3F, with essential fluorine. It was renamed "fluor-liddicoatite", and "liddicoatite" is currently a non-approved species. Some naturally occurring specimens, however, may indeed correspond to the original "liddicoatite", so the name may need to be re-instated if analyses so confirm.

Liddicoatites and most elbaites occur in lithium, cesium, and tantalum rich pegmatites that are almost exclusively related to granitic magmas. At Anjanabonoina, fluor-liddicoatite crystals to 50 cm are found in deeply weathered pegmatites hosted in marble, which probably provides the late-stage enrichment in calcium necessary for the formation of fluor-liddicoatite. Associated minerals include beryl, spodumene, danburite, spessartine, feldspar, mica, magnetite and quartz (R&M 88.4.346-352). The fluor-liddicoatite from here is well-known for the extremely beautiful symmetrical colour zoning which is found in many of the crystals (AM 62.1121-1124).

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