Gaylussite is a relatively soft, hydrated sodium calcium carbonate mineral typically found in evaporite lake deposits. It is known for its distinctive wedge-shaped, monoclinic crystal habit and its tendency to dehydrate into powdery white coatings if not kept in a stable environment.

Hardness

2.5-3

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineraluncommon

Gaylussite

Hardness: 2.5-3
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this gaylussite?

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 gaylussite with a known reference. Gaylussite sits at Mohs 2.5-3 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Gaylussite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Gaylussite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: colorless, white, gray, yellowish.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: wedge-shaped or prismatic crystals, sometimes elongated.

Often confused with

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

How to tell apart: Gaylussite is noticeably harder (Mohs 2.5-3 vs. 1-1.5).

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Often found alongside gaylussite

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

All properties

Chemical formula: Na₂Ca(CO₃)₂·5H₂O
Mohs hardness: 2.5-3
Density: 1.99 g/cm³
Colors: Colorless White Gray Yellowish
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Wedge-shaped or Prismatic Crystals, Sometimes Elongated
Cleavage: Perfect On {110}
Fluorescence: Bright White or Yellow Under LW UV
Rarity: Uncommon
Uses: Collector
Host rock: Evaporite Deposits in Saline Lake Beds
Typical price: $10-50 per specimen

Where rockhounds find gaylussite

Classic worldwide localities

Lake Natron, Tanzania
Searles Lake, California, USA
Laguna del Rey, Mexico
Green River Formation, Wyoming, USA

Field-hunting tip

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

Common questions

How do you identify gaylussite?+

Mohs hardness is 2.5-3. It typically shows a vitreous luster. The streak is white. Common colors include colorless, white, gray, yellowish.

Where is gaylussite found?+

Notable localities include Lake Natron, Tanzania; Searles Lake, California, USA; Laguna del Rey, Mexico; Green River Formation, Wyoming, USA.

How much is gaylussite worth?+

Typical asking prices fall in the range of $10-50 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like gaylussite?+

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

What minerals are found with gaylussite?+

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

What kind of rock does gaylussite form in?+

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

What is gaylussite used for?+

Gaylussite is used in collector.

Find gaylussite on the map

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