Slawsonite is a rare strontium-bearing feldspar that is primarily valued by mineral collectors for its strong blue fluorescence under short-wave UV light. It is typically found as small, clear to white tabular crystals embedded in metamorphosed limestone or calcium-rich silicate rocks.

Hardness

5.5-6.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Semitransparent

mineralrareFeldspar Group family

Slawsonite

Hardness: 5.5-6.5
Luster: Vitreous
Streak: White
Transparency: Semitransparent

Is this slawsonite?

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 slawsonite with a known reference. Slawsonite sits at Mohs 5.5-6.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: colorless, medium gray.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: aggregates, radial, tabular.

Often confused with

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

Often found alongside slawsonite

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

All properties

Chemical formula: SrAl₂Si₂O₈
Mohs hardness: 5.5-6.5
Density: 3.05 g/cm³
Colors: ColorlessMedium gray
Streak: White
Luster: Vitreous
Transparency: Semitransparent
Crystal system: Monoclinic
Crystal habit: Aggregates, radial, tabular
Cleavage: Good on {001}, fair to good on {100}
Fluorescence: Pinkish red purple under SW UV
Rarity: Rare
Uses: Collector
Host rock: In pectolite veinlets in metamorphosed xenoliths (Rendai, Japan); in a xenolith in ultramafic rock (Sarusaka, Japan)

Where rockhounds find slawsonite

Classic worldwide localities

Wallowa Mountains, Wallowa Co., Oregon, USA
Kochi Prefecture, from Sarusaka, Kamagi, Japan
Rendai, Kochi City, Japan
Miyanotani, Hidaka, Japan

Field-hunting tip

Where it forms: In pectolite veinlets in metamorphosed xenoliths (Rendai, Japan); in a xenolith in ultramafic rock (Sarusaka, Japan). If you start seeing calcite, phlogopite, albite in float, you are in the right ground. Typical habit: aggregates, radial, tabular. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify slawsonite?+

Mohs hardness is 5.5-6.5. Luster: vitreous. The streak is white. Common colors include colorless, medium gray.

Where is slawsonite found?+

Notable localities include Wallowa Mountains, Wallowa Co., Oregon, USA; Kochi Prefecture, from Sarusaka, Kamagi, Japan; Rendai, Kochi City, Japan; Miyanotani, Hidaka, Japan.

What rocks look like slawsonite?+

Slawsonite is most often confused with Anorthite, Albite, Celsian. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with slawsonite?+

Slawsonite commonly co-occurs with Calcite, Phlogopite, Albite, Pyrite, Celsian, Cymrite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does slawsonite form in?+

Where it forms: In pectolite veinlets in metamorphosed xenoliths (Rendai, Japan); in a xenolith in ultramafic rock (Sarusaka, Japan). Working float back to the host body is the standard way to chase a fresh occurrence.

What is slawsonite used for?+

Slawsonite is used in collector.

Find slawsonite on the map

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