Londonite Locality: Antsongombato gem mine, FKT Antsentsindrano, Andrembesoa Commune, Betafo District, Vakinankaratra Region , Antananarivo Province , Madagascar ( Locality at mindat.org ) An excellent, gemmy and lustrous, 1.8 cm londonite crystal with exceptional yellow color on matrix from the co-type locality in Madagascar. Londonite is the ultra-rare, cesium-dominant analogue of rhodizite. This is a relatively large, and certainly unusually colorful crystal. One side of the rear of the crystal is cleaved, but it is certainly not detracting given that the display view from teh front is stellar. There are several red tourmaline crystals in the matrix. 4.2 x 3.7 x 2.9 cm — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Londonite
A rare caesium-beryllium aluminosilicate-borate — a mineral that stores caesium in its dense framework.
Intro adapted from Wikipedia (CC BY-SA).
Londonite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula CsBe₄Al₄(B₁₁Be)O₂₈.
It crystallizes in the cubic crystal system (space group P-43m). It is a member of the Rhodizite structural group.
Key properties: Mohs hardness 8; specific gravity 3.34; White streak; Vitreous luster.
IMA symbol Ldn, IMA status: approved, named in 1999.
An uncommon component of granite pegmatites, in the central zones and in miarolitic cavities.
It is found associated with Rhodizite, danburite, elbaite–liddicoatite–schorl, Cs-rich beryl, spodumene, Mn-rich apatite, hambergite, microlite, manganocolumbite, manganotantalite.
The mineral was named to honor Dr. David London (1953–), Professor of Geology and Geophysics, University of Oklahoma, Norman, Oklahoma, USA.