Images
Formula: Ca(Li2Al)Al6(Si6O18)(BO3)3(OH)3F
Cyclosilicate (ring silicate), borosilicate,
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:
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).
Back to Minerals