Jahnsite-(NaFeMg) is a rare secondary phosphate mineral found primarily in altered phosphate-rich granite pegmatites. Collectors typically look for small, distinct yellow-to-brown tabular crystals occurring in vugs associated with other phosphate minerals.

Hardness

3-4

Mohs

Luster

Vitreous

Streak

White

Transparency

Translucent

mineralrareJahnsite Group family

Jahnsite-(NaFeMg)

Hardness: 3-4
Luster: Vitreous
Streak: White
Transparency: Translucent

Is this jahnsite-(nafemg)?

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-(nafemg) with a known reference. Jahnsite-(NaFeMg) sits at Mohs 3-4 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Jahnsite-(NaFeMg) leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Jahnsite-(NaFeMg) typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: yellow, yellowish-brown, brown.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular crystals, subparallel aggregates.

Often confused with

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

Often found alongside jahnsite-(nafemg)

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

All properties

Chemical formula: NaFe²⁺Mg₂Fe³⁺₂(PO₄)₄(OH)₂·8H₂O
Mohs hardness: 3-4
Density: 2.7-2.9 g/cm³
Colors: Yellow Yellowish-brown Brown
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Tabular Crystals, Subparallel Aggregates
Cleavage: Good On {001}
Rarity: Rare
Uses: Collector
Host rock: Granite Pegmatites
Typical price: $50-300 per specimen

Where rockhounds find jahnsite-(nafemg)

Classic worldwide localities

Tip Top Mine, South Dakota, USA
Palermo No. 1 Mine, New Hampshire, USA
Hagendorf-Pleystein, Bavaria, Germany

Field-hunting tip

Look in granite pegmatites country — that is the host setting where jahnsite-(nafemg) typically forms. If you start seeing triphylite, leucophosphite, rockbridgeite in float, you are in the right ground. Field specimens usually show a tabular crystals, subparallel aggregates habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify jahnsite-(nafemg)?+

Mohs hardness is 3-4. It typically shows a vitreous luster. The streak is white. Common colors include yellow, yellowish-brown, brown.

Where is jahnsite-(nafemg) found?+

Notable localities include Tip Top Mine, South Dakota, USA; Palermo No. 1 Mine, New Hampshire, USA; Hagendorf-Pleystein, Bavaria, Germany.

How much is jahnsite-(nafemg) worth?+

Typical asking prices fall in the range of $50-300 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like jahnsite-(nafemg)?+

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

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

Jahnsite-(NaFeMg) commonly co-occurs with Triphylite, Leucophosphite, Rockbridgeite, Fairfieldite. Spotting any of these in float or country rock is a useful trip signal.

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

Jahnsite-(NaFeMg) typically forms in granite pegmatites. Working float back to the host body is the standard way to chase a fresh occurrence.

What is jahnsite-(nafemg) used for?+

Jahnsite-(NaFeMg) is used in collector.

Find jahnsite-(nafemg) on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.