Iowaite is a rare layered double hydroxide mineral typically found as green to blue-green platy aggregates in serpentinized rocks. It is highly unstable when exposed to air and can dehydrate or alter rapidly, making it a challenging but rewarding find for mineral collectors.

Hardness

1.5-2.5

Mohs

Luster

Greasy

Streak

White

Transparency

Opaque to translucent

mineralrareHydrotalcite Supergroup family

Iowaite

Hardness: 1.5-2.5
Luster: Greasy
Streak: White
Transparency: Opaque to translucent

Is this iowaite?

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 iowaite with a known reference. Iowaite sits at Mohs 1.5-2.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: greasy.
4
Match the color range
Compare against the expected color range: bluish green, greenish white, honey yellow.
5
Look at form & habit
Crystal system: trigonal. Typical habit: platy.

Often confused with

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

mineral

Hydrotalcite

Mohs 2

How to tell apart: Luster reads greasy on Iowaite and satiny to greasy or waxy on Hydrotalcite.

How to tell apart: Luster reads greasy on Iowaite and waxy to vitreous, may be pearly on Pyroaurite.

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Often found alongside iowaite

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

All properties

Chemical formula: Mg₆Fe₂(OH)₁₆Cl₂·4H₂O
Mohs hardness: 1.5-2.5
Density: 2.09 g/cm³
Colors: Bluish green Greenish white Honey yellow
Streak: White
Luster: Greasy
Transparency: Opaque to translucent
Crystal system: Trigonal
Crystal habit: Platy
Cleavage: {0001}, perfect
Rarity: Rare
Uses: Collector, Scientific research
Host rock: An alteration product of serpentine

Where rockhounds find iowaite

Classic worldwide localities

Drill core from the Precambrian basement of Sioux Co., Iowa, USA
Phalaborwa mine, Transvaal, South Africa
Komsomolsk mine, Talnakh, Noril’sk region, western Siberia, Russia
Almalyk district, Uzbekistan
Sea floor sediments in the Bonin-Mariana area, Pacific Ocean
Mount Keith nickel deposit, 400 km north-northwest of Kalgoorlie, Western Australia

Field-hunting tip

Where it forms: An alteration product of serpentine. If you start seeing chrysotile, dolomite, brucite in float, you are in the right ground. Typical habit: platy. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify iowaite?+

Mohs hardness is 1.5-2.5. Luster: greasy. The streak is white. Common colors include bluish green, greenish white, honey yellow.

Where is iowaite found?+

Notable localities include Drill core from the Precambrian basement of Sioux Co., Iowa, USA; Phalaborwa mine, Transvaal, South Africa; Komsomolsk mine, Talnakh, Noril’sk region, western Siberia, Russia; Almalyk district, Uzbekistan; Sea floor sediments in the Bonin-Mariana area, Pacific Ocean.

What rocks look like iowaite?+

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

What minerals are found with iowaite?+

Iowaite commonly co-occurs with Chrysotile, Dolomite, Brucite, Calcite, Magnesite, Pyrite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does iowaite form in?+

Where it forms: An alteration product of serpentine. Working float back to the host body is the standard way to chase a fresh occurrence.

What is iowaite used for?+

Iowaite is used in collector, scientific research.

Find iowaite on the map

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