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Formula: Ca8Mg(SiO4)4Cl2
Nesosilicate (insular SiO4 groups)
Crystal System: Isometric
Specific gravity: 3.03 calculated
Streak: Light amber
Colour: Orange-brown to amber, rarely green
Luminescence: Not fluorescent under long wave or short wave UV
Environments
Localities
At the type locality, the Caspar quarry, Ettringen, Vordereifel, Mayen-Koblenz, Rhineland-Palatinate, Germany,
rondorfite was found together with almarudite and
wadalite in an active quarry at the Bellerberg volcano lava field.
Rondorfite and the containing assemblage were formed during a metasomatic modification of
limestone xenoliths enclosed in a Quaternary (2.58 million
years ago to the present) leucite -
tephrite lava. Rondorfite is associated with
ettringite-thaumasite,
mayenite, ternesite,
cuspidine, larnite,
calcio-olivine, tobermorite,
portlandite, hydrocalumite,
a member of the ellestadite series, and minor amounts of
magnetite and hematite. The type
material consists of anhedral grains intergrown with ternesite, both embedded
in a carbonate-quartz matrix containing subordinate amounts of
hematite and magnetite.
Rondorfite grains are anhedral, less than 0.3 mm in diameter, and show orange-brown to amber colour, vitreous
lustre, and a light amber streak
(Mihajlović, T., C. L. Lengauer, T. Ntaflos, U. Kolitsch and E. Tillmanns (2004) Two new minerals rondorfite,
Ca8Mg[SiO4]4Cl2, and almarudite, K(ٱ,Na)2(Mn,Fe,Mg)2(Be,Al)3[Si12O30], and a study of iron-rich wadalite,
Ca12[(Al8Si4Fe2)O32]Cl6, from the Bellerberg (Bellberg) volcano).
Rondorfite from the Caspar Quarry - Image
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