Coombsite is a rare phyllosilicate mineral typically found in metamorphosed zinc-rich deposits. It is best identified by its brownish platy appearance, which often forms dense, micaceous aggregates associated with other rare zinc minerals.

Hardness

2.5

Mohs

Luster

Pearly

Streak

White

Transparency

Translucent

mineralrareSerpentine Group family

Coombsite

Hardness: 2.5
Luster: Pearly
Streak: White
Transparency: Translucent

Is this coombsite?

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 coombsite with a known reference. Coombsite 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. Coombsite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Coombsite typically shows a pearly luster.
4
Match the color range
Compare against the expected color range: yellow, brown, black.
5
Look at form & habit
Crystal system: trigonal. Typical habit: platy aggregates.

Often confused with

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

mineral

Serpentine

Mohs 2.5-5.5

How to tell apart: Luster reads pearly on Coombsite and greasy on Serpentine.

Often found alongside coombsite

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

All properties

Chemical formula: (Mn,Mg,Zn)₃(Si,Al,Fe)₂O₅(OH)₄
Mohs hardness: 2.5
Density: 2.7-2.9 g/cm³
Colors: Yellow Brown Black
Streak: White
Luster: Pearly
Transparency: Translucent
Crystal system: Trigonal
Crystal habit: Platy Aggregates
Cleavage: Perfect Basal
Rarity: Rare
Uses: Collector
Host rock: Metamorphosed Zinc Ore Deposits
Typical price: $50-300 per specimen depending on size and association

Where rockhounds find coombsite

Classic worldwide localities

Franklin, New Jersey, USA
Sterling Hill, New Jersey, USA

Field-hunting tip

Look in metamorphosed zinc ore deposits country, the host setting where coombsite typically forms. If you start seeing willemite, franklinite, zincite in float, you are in the right ground. Field specimens usually show a platy aggregates habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify coombsite?+

Mohs hardness is 2.5. It typically shows a pearly luster. The streak is white. Common colors include yellow, brown, black.

Where is coombsite found?+

Notable localities include Franklin, New Jersey, USA; Sterling Hill, New Jersey, USA.

How much is coombsite worth?+

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

What rocks look like coombsite?+

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

What minerals are found with coombsite?+

Coombsite commonly co-occurs with Willemite, Franklinite, Zincite, Gahnite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does coombsite form in?+

Coombsite typically forms in metamorphosed zinc ore deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is coombsite used for?+

Coombsite is used in collector.

Find coombsite on the map

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