Kayrobertsonite is a rare manganese zinc phosphate mineral discovered in granite pegmatite environments. It typically forms as small, pale yellow tabular crystals and is primarily sought by advanced mineral collectors specializing in phosphate species.

Hardness

3.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrarePhosphate Group family

Kayrobertsonite

Hardness: 3.5
Luster: Vitreous
Streak: White
Transparency: Transparent

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Is this kayrobertsonite?

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 kayrobertsonite with a known reference. Kayrobertsonite sits at Mohs 3.5 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Kayrobertsonite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Kayrobertsonite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: yellow, pale yellow.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular crystals.

Often confused with

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

Often found alongside kayrobertsonite

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

All properties

Chemical formula: Mn₂Zn₂(PO₄)₂(OH)₂·2H₂O
Mohs hardness: 3.5
Density: 2.85 g/cm³
Colors: Yellow Pale Yellow
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Tabular Crystals
Cleavage: Perfect
Rarity: Rare
Uses: Collector
Host rock: Granite Pegmatites
Typical price: $50-300 per specimen

Where rockhounds find kayrobertsonite

Classic worldwide localities

Tip Top Mine, South Dakota, USA

Field-hunting tip

Look in granite pegmatites country — that is the host setting where kayrobertsonite typically forms. If you start seeing triphylite, hureaulite, eosphorite in float, you are in the right ground. Field specimens usually show a tabular crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify kayrobertsonite?+

Mohs hardness is 3.5. It typically shows a vitreous luster. The streak is white. Common colors include yellow, pale yellow.

Where is kayrobertsonite found?+

Notable localities include Tip Top Mine, South Dakota, USA.

How much is kayrobertsonite 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 kayrobertsonite?+

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

What minerals are found with kayrobertsonite?+

Kayrobertsonite commonly co-occurs with Triphylite, Hureaulite, Eosphorite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does kayrobertsonite form in?+

Kayrobertsonite typically forms in granite pegmatites. Working float back to the host body is the standard way to chase a fresh occurrence.

What is kayrobertsonite used for?+

Kayrobertsonite is used in collector.

Find kayrobertsonite on the map

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