Julgoldite

julgoldite

babingtonite

ilvaite

epistilbite

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Formula:
julgoldite-(Fe2+): Ca₂Fe²⁺Fe³⁺₂(Si₂O₇)(SiO₄)(OH)₂.H₂O
julgoldite-(Fe3+): Ca₂Fe³⁺Fe³⁺₂(Si₂O₇)(SiO₄)O(OH).H₂O
julgoldite-(Mg): Ca₂MgFe³⁺₂(Si₂O₇)(SiO₄)(OH)₂.H₂O
Sorosilicates (Si₂O₇ groups), julgoldite subgroup of the pumpellyite group, julgoldite-(Fe2+) forms a series with pumpellyite-(Fe²⁺) and pumpellyite-(Mg)
Crystal System: Monoclinic
Specific gravity: 3.6
Hardness: 4½
Streak: Fe3+ Greenish-olive with a bluish tinge
Colour: Black, Greenish black, Green
Common impurities: julgoldite-(Mg): K
Environments:

Metamorphic environments

Julgoldite-(Fe2+) is associated with apophyllite, baryte, hematite, magnetite, ilvaite, calcite, quartz, chlorite, prehnite, epistilbite, stilbite, pectolite, laumontite, babingtonite and titanite (HOM).

Localities

In the Jalgaon District, Nashik Division, Maharashtra, India, julgoldite occurs as black overgrowths on hairlike mordenite crystals to 3 cm long, or julgoldite pseudomorphs after mordenite (Minrec 34.1.50-51).

At Savda, Sawade Pr Chandsar, Jalgaon District, Nashik Division, Maharashtra, India, specimens have been found of stilbite heavily coated and included by dull greenish black julgoldite in microcrystals and sprays to 2 cm (Minrec 35.3.256).

At Mahad, Raigad District, Konkan Division, Maharashtra, India, julgoldite occurs as dark green crystals covering mordenite (Minrec 34.1.50-51).

At Bombay-Malad, Mumbai Suburban district, Maharashtra, India, julgoldite-(Fe) occurs rarely as platy black crystals up to 2 cm long, associated with clinochlore, quartz, prehnite, calcite and laumontite. The sequence of crystallisation was clinochlore - julgoldite - prehnite - quartz (Minrec 34.1.50-51).

The Långban mine, Långban Ore District, Filipstad, Värmland County, Sweden, is the type locality both for julgoldite-(Fe2+) and for julgoldite-(Fe3+).
Here julgoldite-(Fe2+) occurs filling cavities and embedded in large plates of apophyllite and minor baryite, which constitute a fissure filling in granular hematite-magnetite ore (AM 56.2157-2158).
Julgoldite-(Fe3+) occurs as a fracture filling in hematite-magnetite ore (Webmin).

The type locality for julgoldite-(Mg) is Sugashima, Toba City, Mie Prefecture, Japan.

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