Mikasaite is an extremely rare iron-aluminum sulfate mineral that forms in the combustion zones of coal mine fires. It typically presents as delicate, tiny tabular crystals or powdery white crusts associated with other fumarolic minerals. Due to its formation in specific high-temperature environments, collectors typically encounter it only from its type locality in Japan.

Hardness

Mohs

Luster

Earthy

Streak

White to pale brown

Transparency

Semitransparent

mineralrare

Mikasaite

Hardness: 2
Luster: Earthy
Streak: White to pale brown
Transparency: Semitransparent

No image

Is this mikasaite?

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 mikasaite with a known reference. Mikasaite 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. Streak: white to pale brown.
3
Read the luster
Hold the specimen under a strong light. Luster: earthy.
4
Match the color range
Compare against the expected color range: white, light brown.
5
Look at form & habit
Crystal system: trigonal. Typical habit: spherical.

Often confused with

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

mineral

Millosevichite

Mohs 1.5

How to tell apart: Streak differs, so Mikasaite leaves white to pale brown, Millosevichite leaves red; luster reads earthy on Mikasaite and vitreous on Millosevichite.

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Often found alongside mikasaite

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

All properties

Chemical formula: Fe₂(SO₄)₃
Mohs hardness: 2
Density: 3.06 g/cm³
Colors: White Light brown
Streak: White to pale brown
Luster: Earthy
Transparency: Semitransparent
Crystal system: Trigonal
Crystal habit: Spherical
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: A sublimate around a burning coal-gas escape fracture, formed at > 300°C

Where rockhounds find mikasaite

Classic worldwide localities

Ikushunbetsu, near Mikasa, Hokkaido, Japan

Field-hunting tip

Where it forms: A sublimate around a burning coal-gas escape fracture, formed at > 300°C. If you start seeing sulphur, alunogen, halotrichite in float, you are in the right ground. Typical habit: spherical. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify mikasaite?+

Mohs hardness is 2. Luster: earthy. The streak is white to pale brown. Common colors include white, light brown.

Where is mikasaite found?+

Notable localities include Ikushunbetsu, near Mikasa, Hokkaido, Japan.

What rocks look like mikasaite?+

Mikasaite is most often confused with Millosevichite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with mikasaite?+

Mikasaite commonly co-occurs with Sulphur, Alunogen, Halotrichite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does mikasaite form in?+

Where it forms: A sublimate around a burning coal-gas escape fracture, formed at > 300°C. Working float back to the host body is the standard way to chase a fresh occurrence.

What is mikasaite used for?+

Mikasaite is used in collector.

Find mikasaite on the map

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