Julgoldite-(Fe3+) is a rare member of the pumpellyite group, typically occurring as small, dark, tabular crystals within volcanic rock cavities. Collectors generally find it as part of mineral assemblages in basalt, often associated with secondary minerals like quartz and prehnite.

Hardness

4.5

Mohs

Luster

Vitreous

Streak

Greenish olive

Transparency

Opaque

mineralrarePumpellyite Group family

Julgoldite-(Fe3+)

Hardness: 4.5
Luster: Vitreous
Streak: Greenish olive
Transparency: Opaque

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Is this julgoldite-(fe3+)?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch julgoldite-(fe3+) with a known reference. Julgoldite-(Fe3+) sits at Mohs 4.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: greenish olive.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: black, brownish black.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular crystals, radiating aggregates.

Often confused with

Julgoldite-(Fe3+) vs. its common look-alikes, and how to tell them apart in the field.

mineral

Epidote

Mohs 6-7

How to tell apart: Epidote is the harder of the two (Mohs 6-7 vs. 4.5); streak differs, so Julgoldite-(Fe3+) leaves greenish olive, Epidote leaves grayish white.

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Often found alongside julgoldite-(fe3+)

Minerals reported to co-occur with julgoldite-(fe3+). Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: Ca₂FeFe₂(Si₂O₇)(SiO₄)O(OH)·H₂O
Mohs hardness: 4.5
Density: 3.55-3.65 g/cm³
Colors: Black Brownish black
Streak: Greenish olive
Luster: Vitreous
Transparency: Opaque
Crystal system: Monoclinic
Crystal habit: Tabular crystals, radiating aggregates
Cleavage: Poor
Rarity: Rare
Uses: Collector
Host rock: basaltic vugs and cavities

Where rockhounds find julgoldite-(fe3+)

Classic worldwide localities

Bombay, India
Kallur, India
Långban, Sweden

Field-hunting tip

Where it forms: basaltic vugs and cavities. If you start seeing quartz, calcite, prehnite in float, you are in the right ground. Typical habit: tabular crystals, radiating aggregates. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify julgoldite-(fe3+)?+

Mohs hardness is 4.5. Luster: vitreous. The streak is greenish olive. Common colors include black, brownish black.

Where is julgoldite-(fe3+) found?+

Notable localities include Bombay, India; Kallur, India; Långban, Sweden.

What rocks look like julgoldite-(fe3+)?+

Julgoldite-(Fe3+) is most often confused with Epidote. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with julgoldite-(fe3+)?+

Julgoldite-(Fe3+) commonly co-occurs with Quartz, Calcite, Prehnite, Apophyllite, Zeolites. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does julgoldite-(fe3+) form in?+

Where it forms: basaltic vugs and cavities. Working float back to the host body is the standard way to chase a fresh occurrence.

What is julgoldite-(fe3+) used for?+

Julgoldite-(Fe3+) is used in collector.

Find julgoldite-(fe3+) on the map

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