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

White

Transparency

Transparent

mineralrare

Henmilite

Hardness: 2.5
Luster: Vitreous
Streak: 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. Henmilite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Henmilite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: blue, violet-blue.
5
Look at form & habit
Crystal system: triclinic. Typical habit: tabular 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); streak differs — Henmilite leaves white, Azurite leaves light blue; luster reads vitreous on Henmilite and vitreous to dull on Azurite.

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: 2.54 g/cm³
Colors: Blue Violet-blue
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Triclinic
Crystal habit: Tabular Crystals
Cleavage: Perfect On {001}
Rarity: Rare
Uses: Collector
Host rock: Skarn Deposits in Contact Metamorphic Zones
Typical price: $50-300+ per specimen depending on crystal quality

Where rockhounds find henmilite

Classic worldwide localities

Fuka Mine, Okayama Prefecture, Japan

Field-hunting tip

Look in skarn deposits in contact metamorphic zones country — that is the host setting where henmilite typically forms. If you start seeing fukalite, reyerite, tobermorite 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 henmilite?+

Mohs hardness is 2.5. It typically shows a vitreous luster. The streak is white. Common colors include blue, violet-blue.

Where is henmilite found?+

Notable localities include Fuka Mine, Okayama Prefecture, Japan.

How much is henmilite worth?+

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

Is henmilite safe to handle?+

It contains toxic constituents. Contains copper; wash hands thoroughly after handling and avoid ingestion or inhalation of dust. Handle with care, avoid grinding or breathing dust, and store separately.

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 Fukalite, Reyerite, Tobermorite, Portlandite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does henmilite form in?+

Henmilite typically forms in skarn deposits in contact metamorphic zones. 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.