Jahnsite-(CaMnMg) is a rare secondary phosphate mineral found primarily in complex granite pegmatites. Collectors should look for distinct, glassy, yellow-to-brown prismatic crystals often resting on weathered phosphate cores or associated with other rare phosphate species.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Translucent

mineralrareJahnsite Group family

Jahnsite-(CaMnMg)

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

Is this jahnsite-(camnmg)?

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-(camnmg) with a known reference. Jahnsite-(CaMnMg) 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. Jahnsite-(CaMnMg) leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Jahnsite-(CaMnMg) typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: yellow, yellow-brown, brown, amber.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular, prismatic crystals or encrusting aggregates.

Often confused with

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

Often found alongside jahnsite-(camnmg)

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

All properties

Chemical formula: CaMnMg₂Fe³⁺₂(PO₄)₄(OH)₂·8H₂O
Mohs hardness: 4
Density: 2.63-2.73 g/cm³
Colors: Yellow Yellow-brown Brown Amber
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Tabular, Prismatic Crystals or Encrusting Aggregates
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Granite Pegmatites
Typical price: $50-300 per specimen

Where rockhounds find jahnsite-(camnmg)

Classic worldwide localities

Tip Top Mine, South Dakota, USA
Palermo No. 1 Mine, New Hampshire, USA
Mangualde, Portugal

Field-hunting tip

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

Common questions

How do you identify jahnsite-(camnmg)?+

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

Where is jahnsite-(camnmg) found?+

Notable localities include Tip Top Mine, South Dakota, USA; Palermo No. 1 Mine, New Hampshire, USA; Mangualde, Portugal.

How much is jahnsite-(camnmg) 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-(camnmg)?+

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

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

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

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

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

What is jahnsite-(camnmg) used for?+

Jahnsite-(CaMnMg) is used in collector.

Find jahnsite-(camnmg) on the map

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