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, 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.