Motukoreaite is a rare layered double hydroxide mineral typically found as white or pale blue platy, micaceous crystals in volcanic settings. It is often identified in basaltic cavities and is known for its perfect basal cleavage, similar to other members of the hydrotalcite group.
Is this motukoreaite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch motukoreaite with a known reference. Motukoreaite sits at Mohs 1-1.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: dull.
- 4Match the color rangeCompare against the expected color range: white, yellow green, light yellow.
- 5Look at form & habitCrystal system: trigonal. Typical habit: fibrous, radial.
Often confused with
Motukoreaite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside motukoreaite
Minerals reported to co-occur with motukoreaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mg₆Al₃(OH)₁₈[Na(H₂O)₆](SO₄)₂·6H₂O
- Mohs hardness
- 1-1.5
- Density
- 1.43-1.53 g/cm³
- Streak
- White
- Luster
- Dull
- Transparency
- Semitransparent
- Crystal system
- Trigonal
- Crystal habit
- Fibrous, radial
- Cleavage
- Good on {0001}, perhaps a parting
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Relatively common in assemblages formed by reaction of basalt volcanoclastics with sea-water; in cavities in a haüyne-nephelinite
Where rockhounds find motukoreaite
Classic worldwide localities
- Brown’s Island (Motukorea), Waitemata Harbour, Auckland, New Zealand
- Island of Surtsey, and the Great Meteor and Josephine seamounts, North Atlantic, and along the mid-Atlantic Ridge
- Northwest of the Emile Baudot Bank, western Mediterranean
- Axial Rift, Red Sea
- Stradner Kogel, south of Gleichenberg, Austria
Field-hunting tip
Where it forms: Relatively common in assemblages formed by reaction of basalt volcanoclastics with sea-water; in cavities in a haüyne-nephelinite. If you start seeing olivine, pyroxene, calcic feldspar in float, you are in the right ground. Typical habit: fibrous, radial. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify motukoreaite?+
Where is motukoreaite found?+
What rocks look like motukoreaite?+
What minerals are found with motukoreaite?+
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What is motukoreaite used for?+
Find motukoreaite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
