Kruijenite is an extremely rare sulfate mineral originally discovered in the Netherlands. It typically forms small, clear, tabular crystals within altered limestone xenoliths and is primarily sought after by advanced systematic mineral collectors.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Kruijenite

Hardness: 2
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this kruijenite?

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 kruijenite with a known reference. Kruijenite sits at Mohs 2 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Kruijenite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Kruijenite 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: tabular crystals.

Often confused with

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

Often found alongside kruijenite

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

All properties

Chemical formula: CaAl₂(OH)₄(SO₄)·2H₂O
Mohs hardness: 2
Density: 2.1 g/cm³
Colors: Colorless White
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Triclinic
Crystal habit: Tabular Crystals
Cleavage: Perfect
Rarity: Rare
Uses: Collector
Host rock: Metamorphosed Limestone Inclusions in Alkaline Igneous Rocks
Typical price: $50-300 per specimen

Where rockhounds find kruijenite

Classic worldwide localities

Kruijen quarry, Limburg, Netherlands

Field-hunting tip

Look in metamorphosed limestone inclusions in alkaline igneous rocks country — that is the host setting where kruijenite typically forms. If you start seeing gypsum, ettringite, thaumasite in float, you are in the right ground. Field specimens usually show a tabular crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify kruijenite?+

Mohs hardness is 2. It typically shows a vitreous luster. The streak is white. Common colors include colorless, white.

Where is kruijenite found?+

Notable localities include Kruijen quarry, Limburg, Netherlands.

How much is kruijenite worth?+

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

What rocks look like kruijenite?+

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

What minerals are found with kruijenite?+

Kruijenite commonly co-occurs with gypsum, ettringite, thaumasite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does kruijenite form in?+

Kruijenite typically forms in metamorphosed limestone inclusions in alkaline igneous rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is kruijenite used for?+

Kruijenite is used in collector.

Find kruijenite on the map

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