What is Julgoldite-(Fe3+)?
Julgoldite-(Fe3+) is an iron-rich epidote-group silicate, usually dark green to brown and found in low-temperature alteration and zeolite-related assemblages.
Mineralogy and crystal structure
Reference formula: Ca2Fe3+Fe2+(Si2O6)(SiO4)(OH)2. Julgoldite-(Fe3+) has a monoclinic epidote-group structure with mixed iron valence. The end-member label matters because natural julgoldite compositions can include substitutions and related Fe2+- or Mg-dominant members. Julgoldite-(Fe3+) is classified with silicates and has a monoclinic crystal system. Typical hardness is 5–6 on the Mohs scale and specific gravity is approximately 3.4–3.6.
Colour, lustre and habit
Typical colours include green, brown, black, yellow-brown. The usual fibrous, prismatic, radiating habit and vitreous, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Julgoldite-(Fe3+) forms in or is associated with hydrothermal veins, altered basalts, cavities and low-grade metamorphic rocks. Important documented localities include India, Scotland, Sweden, Italy, Japan and the United States.
A dark green epidote-group specialist
Julgoldite-(Fe3+) is ideal for collectors who enjoy the fine print of mineral classification. Its subdued green-brown colour becomes more interesting when the specimen is read alongside the alteration assemblage and the chemistry of iron oxidation.
The appeal of a precise name
For many collectors, a carefully resolved species name is part of the beauty: it turns a dark green aggregate into a record of chemistry and geological conditions. That is an educational value, not a promise of personal effects.
Collecting and care
Protect fibrous aggregates and cleavage edges; retain analytical and locality information when the end-member assignment is important.
