Walstromite is a rare barium calcium silicate mineral most notably found in the sanbornite-bearing metamorphic rocks of Fresno County, California. It is highly prized by collectors for its brilliant reddish-orange fluorescence under short-wave ultraviolet light. It typically occurs as small, colorless, platy crystals or granular masses embedded within larger mineral assemblages.

Hardness

3.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Walstromite

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

Is this walstromite?

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 walstromite with a known reference. Walstromite 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. Walstromite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Walstromite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: colorless, white.
5
Look at form & habit
Crystal system: triclinic. Typical habit: platy crystals, granular aggregates.

Often confused with

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

mineral

Sanbornite

Mohs 5

How to tell apart: Sanbornite is the harder of the two (Mohs 5 vs. 3.5).

Often found alongside walstromite

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

All properties

Chemical formula: BaCa₂(Si₃O₉)
Mohs hardness: 3.5
Density: 3.39 g/cm³
Colors: Colorless White
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Triclinic
Crystal habit: Platy Crystals, Granular Aggregates
Cleavage: Good On {001}
Fluorescence: Bright Reddish-orange Under SW UV
Rarity: Rare
Uses: Collector, Scientific Research
Host rock: Metamorphosed Limestone Inclusions in Sanbornite-bearing Rocks
Typical price: $50-300 per specimen depending on size and crystal quality

Where rockhounds find walstromite

Classic worldwide localities

Rush Creek, Fresno County, California, USA
Big Creek, Fresno County, California, USA

Field-hunting tip

Look in metamorphosed limestone inclusions in sanbornite-bearing rocks country — that is the host setting where walstromite typically forms. If you start seeing sanbornite, fresnoite, quartz in float, you are in the right ground. Field specimens usually show a platy crystals, granular aggregates habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify walstromite?+

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

Where is walstromite found?+

Notable localities include Rush Creek, Fresno County, California, USA; Big Creek, Fresno County, California, USA.

How much is walstromite worth?+

Typical asking prices fall in the range of $50-300 per specimen depending on size and crystal quality. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like walstromite?+

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

What minerals are found with walstromite?+

Walstromite commonly co-occurs with Sanbornite, Fresnoite, Quartz, K-feldspar. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does walstromite form in?+

Walstromite typically forms in metamorphosed limestone inclusions in sanbornite-bearing rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is walstromite used for?+

Walstromite is used in collector, scientific research.

Find walstromite on the map

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