Calderite Garnet: Gemstone Information
Name approved by the CNMMN of the IMA. Named after James Calder, an early writer on the geology of India; name first applied to a rock, later transferred to its predominant mineral.
Found in regionally metamorphosed siliceous iron and manganese-rich formations. Type locality is at Otjosondu, Namibia, and at Usakos, Namibia. In Katkamsandi, Hazaribagh district, India, this rare garnet occurs as brownish vitreous masses scattered in matrix. Additionally it occurs at Bihar, and at Netra, Balaghat district, Madhya Pradesh, India. Also reported as dark yellow to reddish yellow.
Whilst compositions approaching ideal calderite are unknown, a complete solid solution exists between calderite, andradite and spessartine. Thus the calderite molecule is more likely to be found in calderitic andradite and
calderitic spessartine, where its presence will affect the properties of these species.
Refractive Index – 1.872–1.890 (natural), and 1.97 (calculated for pure calderite). SG – 4.45 (pure calderite).
Not reported in any gem material to date.