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Formula: CsBe4Al4(B11Be)O28
Megaborate of cesium,
beryllium and aluminium, forms a series with
rhodizite
Crystal System: Isometric
Specific gravity: 3.34 measured, 3.42 calculated
Hardness: 8
Streak: White
Colour: Colourless, white, sulphur-yellow, pale yellow, pale yellow-green
Luminescence: Weak yellow-green fluorescence under short wave UV
Electrical: Strongly piezoelectric and pyroelectric
Environments
Londonite is an uncommon component of granite
pegmatites, in the central zones and in miarolitic cavities.
Associated minerals include rhodizite,
danburite, elbaite –
liddicoatite – schorl,
cesium-rich beryl,
spodumene, manganese-rich
apatite, hambergite,
microlite, columbite-(Mn),
tantalite-(Mn), behierite,
hafnian zircon, albite,
microcline and quartz
(HOM).
Localities
At the type locality, the Antandrokomby pegmatite, Manandona Valley, Sahatsiho Ambohimanjaka, Ambositra District,
Amoron'i Mania, Madagascar, londonite, the cesium-dominant analogue of
rhodizite, occurs with rhodizite
in the inner zones and in miarolitic cavities of the highly evolved
granitic
pegmatite rich in red
tourmaline. Associated minerals include
microcline, quartz,
albite, elbaite –
liddicoatite – schorl,
cesium-rich beryl,
spodumene, danburite,
manganese-rich fluorapatite,
hambergite, microlite,
columbite-(Mn),
tantalite-(Mn),
béhierite and
hafnian zircon. Londonite occurs as equidimensional translucent to
transparent crystals a few millimeters across, and exceptionally up to 7 cm
(CM 39.3.747–755).
Londonite from the Antandrokomby pegmatite -
Image
At the Ministerskaya Yama Pit, Sarapulka, Beryozovsky, Sverdlovsk Oblast, Russia and Mor's Pit, Shaitanka District,
Rezhevsky District, Sverdlovsk Oblast, Russia, three old specimens, collected in the 19th century and now deposited in
the Fersman Mineralogical Museum, Moscow, are labeled as rhodizite. All are Cs-dominant (Cs>K) and must now be
considered to be londonite
(CM 48.2.241–254).
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