Jahnsite-(MnMnZn) is a rare phosphate mineral found in phosphate-rich granite pegmatites. Collectors typically look for small, sharp, yellow to brown tabular crystals lining cavities in weathered phosphate nodules.

Hardness

Mohs

Luster

Vitreous to silky

Streak

White

Transparency

Transparent

mineralrareJahnsite Group family

Jahnsite-(MnMnZn)

Hardness: ~4
Luster: Vitreous to silky
Streak: White
Transparency: Transparent

Is this jahnsite-(mnmnzn)?

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 jahnsite-(mnmnzn) with a known reference. Jahnsite-(MnMnZn) sits at Mohs ~4, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous to silky.
4
Match the color range
Compare against the expected color range: yellow, yellow-brown, brown.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular crystals, drusy coatings.

Often confused with

Jahnsite-(MnMnZn) vs. its common look-alikes, and how to tell them apart in the field.

Often found alongside jahnsite-(mnmnzn)

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

All properties

Chemical formula: MnMnZn₂Fe₂(PO₄)₄(OH)₂·8H₂O
Mohs hardness: ~4
Density: 2.89 g/cm³
Colors: Yellow Yellow-brown Brown
Streak: White
Luster: Vitreous to silky
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Tabular crystals, drusy coatings
Cleavage: Good on {001}
Rarity: Rare
Uses: Collector
Host rock: In highly altered (leached and silicified) gossan of an iron-manganese deposit

Where rockhounds find jahnsite-(mnmnzn)

Classic worldwide localities

Herdade dos Pendões manganese and iron mine, 5 km north of Odemira, Beja district, Portugal

Field-hunting tip

Where it forms: In highly altered (leached and silicified) gossan of an iron-manganese deposit. If you start seeing zn-bearing libethenite, quartz, rhodochrosite in float, you are in the right ground. Typical habit: tabular crystals, drusy coatings. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify jahnsite-(mnmnzn)?+

Mohs hardness is ~4. Luster: vitreous to silky. The streak is white. Common colors include yellow, yellow-brown, brown.

Where is jahnsite-(mnmnzn) found?+

Notable localities include Herdade dos Pendões manganese and iron mine, 5 km north of Odemira, Beja district, Portugal.

What rocks look like jahnsite-(mnmnzn)?+

Jahnsite-(MnMnZn) is most often confused with Jahnsite-(CaMnMg). A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with jahnsite-(mnmnzn)?+

Jahnsite-(MnMnZn) commonly co-occurs with Zn-bearing libethenite, Quartz, Rhodochrosite, Santabarbaraite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does jahnsite-(mnmnzn) form in?+

Where it forms: In highly altered (leached and silicified) gossan of an iron-manganese deposit. Working float back to the host body is the standard way to chase a fresh occurrence.

What is jahnsite-(mnmnzn) used for?+

Jahnsite-(MnMnZn) is used in collector.

Find jahnsite-(mnmnzn) on the map

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