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Formula: KNa2Fe2+(Fe2+)2(Ti1.5Fe2+0.5)[Si4O12]2
Phyllosilicate (sheet silicate), a lithium-free member of the
neptunite group
Crystal system: Monoclinic
Specific gravity: 3.20 measured, 3.271 calculated
Hardness: 4½
Streak: Light orange
Colour: Darl brownish red
Luminescence: No fluorescence was observed under either long wave or short wave UV
Solubility: Insoluble in concentrated hydrochloric acid at room temperature
Environments
Volcanic igneous environments
Metamorphic environments
Rotherkopfite is a new mineral, approved in 2023 and to date (August 2025) reported only from the type
locality.
Localities
At the type locality, Rother Kopf, Roth, Gerolstein, Gerolstein, Vulkaneifel, Rhineland-Palatinate, Germany,
rotherkopfite occurs as equant to tabular crystals, up to about 0.2 mm in size, in cavities in a xenolith
embedded in a vesicular alkaline basalt. It is presumed to have formed
as the result of
contact metasomatism of the xenolith by
the alkaline basalt melt. Associated minerals include
fluorophlogopite,
potassic-fluoro-richterite,
potassic-magnesio-fluoro-arfvedsonite,
quartz and sanidine
(Mindat).
Rotherkopfite from Rother Kopf - Image
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