Gatehouseite is an extremely rare manganese phosphate mineral found in complex granite pegmatites. It typically forms attractive, orange, bladed crystals in radial aggregates that are highly sought after by systematic mineral collectors.

Hardness

Mohs

Luster

Adamantine

Streak

Pale yellow

Transparency

Transparent

mineralrare

Gatehouseite

Hardness: ~4
Luster: Adamantine
Streak: Pale yellow
Transparency: Transparent

Is this gatehouseite?

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 gatehouseite with a known reference. Gatehouseite 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: pale yellow.
3
Read the luster
Hold the specimen under a strong light. Luster: adamantine.
4
Match the color range
Compare against the expected color range: yellow, pale orange.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: bladed crystals, radial sprays.

Often confused with

Gatehouseite vs. its common look-alikes, and how to tell them apart in the field.

mineral

Fairfieldite

Mohs 3.5

How to tell apart: Streak differs, so Gatehouseite leaves pale yellow, Fairfieldite leaves white; luster reads adamantine on Gatehouseite and pearly to subadamantine, vitreous on the {001} cleavage on Fairfieldite.

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Often found alongside gatehouseite

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

All properties

Chemical formula: Mn₅(PO₄)₂(OH)₄
Mohs hardness: ~4
Density: 3.74 g/cm³
Colors: YellowPale orange
Streak: Pale yellow
Luster: Adamantine
Transparency: Transparent
Crystal system: Orthorhombic
Crystal habit: Bladed crystals, radial sprays
Cleavage: On {010}, distinct
Rarity: Rare
Uses: Collector
Host rock: As a secondary mineral in cavities in a sedimentary Fe–Mn deposit, probably formed by reaction of phosphorus-rich fluids with hausmannite at low temperature

Where rockhounds find gatehouseite

Classic worldwide localities

Iron Monarch quarry, Iron Knob, South Australia

Field-hunting tip

Where it forms: As a secondary mineral in cavities in a sedimentary Fe–Mn deposit, probably formed by reaction of phosphorus-rich fluids with hausmannite at low temperature. If you start seeing arsenoclasite, shigaite, hematite in float, you are in the right ground. Typical habit: bladed crystals, radial sprays. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify gatehouseite?+

Mohs hardness is ~4. Luster: adamantine. The streak is pale yellow. Common colors include yellow, pale orange.

Where is gatehouseite found?+

Notable localities include Iron Monarch quarry, Iron Knob, South Australia.

What rocks look like gatehouseite?+

Gatehouseite is most often confused with Fairfieldite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with gatehouseite?+

Gatehouseite commonly co-occurs with Arsenoclasite, Shigaite, Hematite, Hausmannite, Triploidite, Barite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does gatehouseite form in?+

Where it forms: As a secondary mineral in cavities in a sedimentary Fe–Mn deposit, probably formed by reaction of phosphorus-rich fluids with hausmannite at low temperature. Working float back to the host body is the standard way to chase a fresh occurrence.

What is gatehouseite used for?+

Gatehouseite is used in collector.

Find gatehouseite on the map

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