Kolicite is an extremely rare manganese zinc silicate-arsenate mineral known almost exclusively from the Franklin-Sterling Hill mining district. It is prized by fluorescent mineral collectors for its vivid orange-red reaction under shortwave ultraviolet light.

Hardness

~4.5

Mohs

Luster

Vitreous

Streak

Light orange

Transparency

Semitransparent

mineralrare

Kolicite

Hardness: ~4.5
Luster: Vitreous
Streak: Light orange
Transparency: Semitransparent

Is this kolicite?

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 kolicite with a known reference. Kolicite sits at Mohs ~4.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: light orange.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: yellow orange.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: anhedral grains, massive.

Often confused with

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

mineral

Willemite

Mohs 5.5

How to tell apart: Willemite is the harder of the two (Mohs 5.5 vs. ~4.5); streak differs, so Kolicite leaves light orange, Willemite leaves white.

How to tell apart: Streak differs, so Kolicite leaves light orange, Hodgkinsonite leaves white.

Compare →

Often found alongside kolicite

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

All properties

Chemical formula: Zn₄Mn₇(AsO₄)₂(SiO₄)₂(OH)₈
Mohs hardness: ~4.5
Density: 4.17 g/cm³
Colors: Yellow orange
Streak: Light orange
Luster: Vitreous
Transparency: Semitransparent
Crystal system: Orthorhombic
Crystal habit: Anhedral grains, massive
Cleavage: None
Fluorescence: Bright orange-red under SW UV
Rarity: Rare
Uses: Collector
Host rock: Incrusting willemite-franklinite ore from metamorphosed stratiform zinc orebodies

Where rockhounds find kolicite

Classic worldwide localities

Sterling Hill, Ogdensburg, and at Franklin, Sussex Co., New Jersey, USA

Field-hunting tip

Where it forms: Incrusting willemite-franklinite ore from metamorphosed stratiform zinc orebodies. If you start seeing willemite, franklinite, sonolite in float, you are in the right ground. Typical habit: anhedral grains, massive. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify kolicite?+

Mohs hardness is ~4.5. Luster: vitreous. The streak is light orange. Common colors include yellow orange.

Where is kolicite found?+

Notable localities include Sterling Hill, Ogdensburg, and at Franklin, Sussex Co., New Jersey, USA.

Is kolicite safe to handle?+

Kolicite contains arsenic and calls for real care. Contains arsenic; handle with care and wash hands thoroughly after handling to avoid ingestion or inhalation of dust.

What rocks look like kolicite?+

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

What minerals are found with kolicite?+

Kolicite commonly co-occurs with Willemite, Franklinite, Sonolite, Friedelite, Holdenite, Calcite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does kolicite form in?+

Where it forms: Incrusting willemite-franklinite ore from metamorphosed stratiform zinc orebodies. Working float back to the host body is the standard way to chase a fresh occurrence.

What is kolicite used for?+

Kolicite is used in collector.

Find kolicite on the map

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