Rosemaryite is a rare phosphate mineral member of the wyllieite group, typically found in complex granite pegmatites. It usually forms as small, brownish, equant crystals or irregular masses associated with other phosphate minerals in hydrothermal alteration zones.

Hardness

4-4.5

Mohs

Luster

Resinous

Streak

Greenish white

Transparency

Semitransparent

mineralrareWyllieite Group family

Rosemaryite

Hardness: 4-4.5
Luster: Resinous
Streak: Greenish white
Transparency: Semitransparent

Is this rosemaryite?

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 rosemaryite with a known reference. Rosemaryite sits at Mohs 4-4.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: greenish white.
3
Read the luster
Hold the specimen under a strong light. Luster: resinous.
4
Match the color range
Compare against the expected color range: bluish green, dark green, deep brown, reddish brown.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: massive.

Often confused with

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

How to tell apart: Streak differs, so Rosemaryite leaves greenish white, Wyllieite leaves olive green; luster reads resinous on Rosemaryite and vitreous to submetallic on Wyllieite.

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Often found alongside rosemaryite

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

All properties

Chemical formula: Na(Mn²⁺Fe³⁺)Al(PO₄)₃
Mohs hardness: 4-4.5
Density: 3.6-3.601 g/cm³
Colors: Bluish green Dark greenDeep brownReddish brown
Streak: Greenish white
Luster: Resinous
Transparency: Semitransparent
Crystal system: Monoclinic
Crystal habit: Massive
Cleavage: Observed
Rarity: Rare
Uses: Collector
Host rock: In zoned complex granite pegmatites

Where rockhounds find rosemaryite

Classic worldwide localities

Rock Ridge pegmatite, near Custer, Custer Co., South Dakota, USA
Buranga pegmatite, near Gatumba, Rwanda

Field-hunting tip

Where it forms: In zoned complex granite pegmatites. If you start seeing trolleite, alluaudite, montebrasite in float, you are in the right ground. Typical habit: massive. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify rosemaryite?+

Mohs hardness is 4-4.5. Luster: resinous. The streak is greenish white. Common colors include bluish green, dark green, deep brown, reddish brown.

Where is rosemaryite found?+

Notable localities include Rock Ridge pegmatite, near Custer, Custer Co., South Dakota, USA; Buranga pegmatite, near Gatumba, Rwanda.

What rocks look like rosemaryite?+

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

What minerals are found with rosemaryite?+

Rosemaryite commonly co-occurs with Trolleite, Alluaudite, Montebrasite, Scorzalite, Strengite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does rosemaryite form in?+

Where it forms: In zoned complex granite pegmatites. Working float back to the host body is the standard way to chase a fresh occurrence.

What is rosemaryite used for?+

Rosemaryite is used in collector.

Find rosemaryite on the map

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