Specimen showing calderite garnet crystals on matrix originating from Litzdalen, Sunndal Norway (width approx. 2 cm) — Photo: Astynax · CC BY-SA 3.0
Calderite
A dark reddish-brown manganese-iron member of the garnet group, usually massive and granular.
Intro adapted from Wikipedia (CC BY-SA).
Calderite is an IMA-recognized mineral species in the silicate class, with the chemical formula Mn²⁺₃Fe³⁺₂(SiO₄)₃.
It crystallizes in the cubic crystal system (space group Ia3d). It is a member of the Garnet structural group.
Key properties: Mohs hardness 7; specific gravity 4.05; refractive index 1.872; optically isotropic.
IMA symbol Cdr, grandfathered status — known before the IMA’s founding, named in 1909.
Found in a manganese deposit (Otjosondu, Namibia); in an iron formation (Wabush district, Canada).
It is found associated with Pyrolusite, aegirine, rhodonite, hematite, rhodochrosite, quartz, kutnohorite (Wabush district, Canada).
The name refers to James Calder, an early writer on the geology of India; name first applied to a rock, later transferred to its predominant mineral.