Omsite is a rare nickel iron antimony hydroxide, typically bright to amber-yellow. It occurs in narrow, crystal-lined fractures cutting massive siderite-bearing rock. It was first described from Correc d'en Llinassos, near the village of Oms, Pyrénées-Orientales Department, France.

Hardness

Mohs

Luster

Vitreous to resinous

Streak

Pale yellow

Transparency

Transparent to translucent

mineralrare

Omsite

Hardness: ~3
Luster: Vitreous to resinous
Streak: Pale yellow
Transparency: Transparent to translucent

Is this omsite?

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 omsite with a known reference. Omsite sits at Mohs ~3, 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 yellow.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous to resinous.
4
Match the color range
Compare against the expected color range: amber-yellow, bright.
5
Look at form & habit
Crystal system: trigonal. Typical habit: microcrystalline aggregates.

Often confused with

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

Often found alongside omsite

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

All properties

Chemical formula: Ni₂Fe³⁺(OH)₆[Sb(OH)₆]
Mohs hardness: ~3
Density: 3.378 g/cm³
Colors: Amber-yellowBright
Streak: Pale yellow
Luster: Vitreous to resinous
Transparency: Transparent to translucent
Crystal system: Trigonal
Crystal habit: Microcrystalline aggregates
Cleavage: Poor on {001}
Rarity: Rare
Uses: Collector
Host rock: In narrow, crystal-lined fractures cutting massive siderite-bearing rock

Where rockhounds find omsite

Classic worldwide localities

Correc d’en Llinassos, near the village of Oms, Pyrénées-Orientales Department, France

Field-hunting tip

Where it forms: In narrow, crystal-lined fractures cutting massive siderite-bearing rock. If you start seeing ullmannite, chalcopyrite, siderite in float, you are in the right ground. Typical habit: microcrystalline aggregates. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify omsite?+

Mohs hardness is ~3. Luster: vitreous to resinous. The streak is pale yellow. Common colors include amber-yellow, bright.

Where is omsite found?+

Notable localities include Correc d’en Llinassos, near the village of Oms, Pyrénées-Orientales Department, France.

Is omsite safe to handle?+

Omsite contains antimony and nickel. Contains antimony, which is toxic if ingested or inhaled as dust. Wash hands thoroughly after handling and avoid creating dust.

What rocks look like omsite?+

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

What minerals are found with omsite?+

Omsite commonly co-occurs with Ullmannite, Chalcopyrite, Siderite, Glaukosphaerite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does omsite form in?+

Where it forms: In narrow, crystal-lined fractures cutting massive siderite-bearing rock. Working float back to the host body is the standard way to chase a fresh occurrence.

What is omsite used for?+

Omsite is used in collector.

Find omsite on the map

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