Selwynite is a rare sodium potassium beryllium phosphate. Associated minerals include wardite, eosphorite and montmorillonite. It was first described from a quarry 0.5 km east of Wycheproof, Victoria, Australia.

Hardness

Mohs

Luster

Vitreous

Streak

Pale lavender

Transparency

Transparent

mineralrare

Selwynite

Hardness: 4
Luster: Vitreous
Streak: Pale lavender
Transparency: Transparent

No image

Is this selwynite?

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 selwynite with a known reference. Selwynite 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 lavender.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: deep purplish blue.
5
Look at form & habit
Crystal system: tetragonal. Typical habit: radial.

Often confused with

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

mineral

Fuchsite

Mohs 2.5-3

How to tell apart: Selwynite is noticeably harder (Mohs 4 vs. 2.5-3); streak differs, so Selwynite leaves pale lavender, Fuchsite leaves white; luster reads vitreous on Selwynite and pearly on Fuchsite.

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Often found alongside selwynite

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

All properties

Chemical formula: NaKBeZr₂(PO₄)₄·2H₂O
Mohs hardness: 4
Density: 2.94 g/cm³
Colors: Deep purplish blue
Streak: Pale lavender
Luster: Vitreous
Transparency: Transparent
Crystal system: Tetragonal
Crystal habit: Radial
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Very rare, a cavity filling in veins, formed under reducing conditions during late-stage cooling in granite pegmatite

Where rockhounds find selwynite

Classic worldwide localities

A granite quarry near Wycheproof, NW Victoria, Australia (type locality)

Field-hunting tip

Where it forms: Very rare, a cavity filling in veins, formed under reducing conditions during late-stage cooling in granite pegmatite. If you start seeing wardite, eosphorite, montmorillonite in float, you are in the right ground. Typical habit: radial. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify selwynite?+

Mohs hardness is 4. Luster: vitreous. The streak is pale lavender. Common colors include deep purplish blue.

Where is selwynite found?+

Notable localities include A granite quarry near Wycheproof, NW Victoria, Australia (type locality).

Is selwynite safe to handle?+

Selwynite contains beryllium. Wash your hands afterwards, never grind or breathe the dust, and store it apart from specimens you handle often.

What rocks look like selwynite?+

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

What minerals are found with selwynite?+

Selwynite commonly co-occurs with Wardite, Eosphorite, Montmorillonite, Limonite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does selwynite form in?+

Where it forms: Very rare, a cavity filling in veins, formed under reducing conditions during late-stage cooling in granite pegmatite. Working float back to the host body is the standard way to chase a fresh occurrence.

What is selwynite used for?+

Selwynite is used in collector.

Find selwynite on the map

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