Pirssonite is a rare hydrated sodium calcium carbonate mineral that typically forms as sharp, wedge-shaped or tabular crystals in evaporite environments. It is most famous for its occurrence in the alkaline brine deposits of Searles Lake, where it is found associated with other rare carbonates and sulfates. Collectors prize it for its distinct crystal geometry and transparency, though it is prone to dehydration if kept in very dry conditions.

Hardness

3-3.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Pirssonite

Hardness: 3-3.5
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this pirssonite?

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 pirssonite with a known reference. Pirssonite sits at Mohs 3-3.5 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Pirssonite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Pirssonite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: colorless, white, yellowish.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: tabular to prismatic crystals, often wedge-shaped.

Often confused with

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

Often found alongside pirssonite

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

All properties

Chemical formula: Na₂Ca(CO₃)₂·2H₂O
Mohs hardness: 3-3.5
Density: 2.35 g/cm³
Colors: Colorless White Yellowish
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Orthorhombic
Crystal habit: Tabular to Prismatic Crystals, Often Wedge-shaped
Cleavage: Distinct
Rarity: Rare
Uses: Collector
Host rock: Evaporite Deposits in Alkaline Lake Beds
Typical price: $20-150 per specimen depending on size and quality

Where rockhounds find pirssonite

Classic worldwide localities

Searles Lake, California, USA
Olduvai Gorge, Tanzania
Khibiny Massif, Russia

Field-hunting tip

Look in evaporite deposits in alkaline lake beds country — that is the host setting where pirssonite typically forms. If you start seeing gaylussite, nahcolite, trona in float, you are in the right ground. Field specimens usually show a tabular to prismatic crystals, often wedge-shaped habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify pirssonite?+

Mohs hardness is 3-3.5. It typically shows a vitreous luster. The streak is white. Common colors include colorless, white, yellowish.

Where is pirssonite found?+

Notable localities include Searles Lake, California, USA; Olduvai Gorge, Tanzania; Khibiny Massif, Russia.

How much is pirssonite worth?+

Typical asking prices fall in the range of $20-150 per specimen depending on size and quality. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like pirssonite?+

Pirssonite is most often confused with Gaylussite, Nahcolite, Trona. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with pirssonite?+

Pirssonite commonly co-occurs with Gaylussite, Nahcolite, Trona, Halite, Thenardite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does pirssonite form in?+

Pirssonite typically forms in evaporite deposits in alkaline lake beds. Working float back to the host body is the standard way to chase a fresh occurrence.

What is pirssonite used for?+

Pirssonite is used in collector.

Find pirssonite on the map

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