Henmilite is a rare copper borate mineral characterized by its striking blue, tabular crystals. It is primarily found in the contact metamorphic zones of the Fuka Mine in Japan, often occurring as small crystals within cavities of skarn rock.

Hardness

<2.5

Mohs

Luster

Vitreous

Streak

Pale violet to nearly white

Transparency

Transparent

mineralrare

Henmilite

Hardness: <2.5
Luster: Vitreous
Streak: Pale violet to nearly white
Transparency: Transparent

Is this henmilite?

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 henmilite with a known reference. Henmilite sits at Mohs <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: pale violet to nearly white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: bluish violet.
5
Look at form & habit
Crystal system: triclinic. Typical habit: microscopic crystals.

Often confused with

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

mineral

Azurite

Mohs 3.5-4

How to tell apart: Azurite is the harder of the two (Mohs 3.5-4 vs. <2.5).

How to tell apart: Streak differs, so Henmilite leaves pale violet to nearly white, Chalcanthite leaves white.

Compare →

Often found alongside henmilite

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

All properties

Chemical formula: Ca₂Cu(OH)₄(B(OH)₄)₂
Mohs hardness: <2.5
Density: 2.51 g/cm³
Colors: Bluish violet
Streak: Pale violet to nearly white
Luster: Vitreous
Transparency: Transparent
Crystal system: Triclinic
Crystal habit: Microscopic crystals
Cleavage: Perfect on {001}
Rarity: Rare
Uses: Collector
Host rock: Very rare, in cavities in borate veins in contact-metasomatized limestone

Where rockhounds find henmilite

Classic worldwide localities

Fuka, near Bicchu, Okayama Prefecture, Japan

Field-hunting tip

Where it forms: Very rare, in cavities in borate veins in contact-metasomatized limestone. If you start seeing pentahydroborite, tenorite, sillenite in float, you are in the right ground. Typical habit: microscopic crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify henmilite?+

Mohs hardness is <2.5. Luster: vitreous. The streak is pale violet to nearly white. Common colors include bluish violet.

Where is henmilite found?+

Notable localities include Fuka, near Bicchu, Okayama Prefecture, Japan.

Is henmilite safe to handle?+

Henmilite contains copper. Contains copper; wash hands thoroughly after handling and avoid ingestion or inhalation of dust.

What rocks look like henmilite?+

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

What minerals are found with henmilite?+

Henmilite commonly co-occurs with Pentahydroborite, Tenorite, Sillenite, Bultfonteinite, Cuspidine, Thaumasite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does henmilite form in?+

Where it forms: Very rare, in cavities in borate veins in contact-metasomatized limestone. Working float back to the host body is the standard way to chase a fresh occurrence.

What is henmilite used for?+

Henmilite is used in collector.

Find henmilite on the map

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