Irhtemite is a rare calcium-magnesium arsenate mineral known primarily from the cobalt-ore deposits of the Bou Azzer district in Morocco. It typically forms delicate, transparent tabular crystals or crusts that are often associated with other rare secondary arsenate minerals in the oxidation zone of cobalt-nickel veins.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Irhtemite

Hardness: 3
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this irhtemite?

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 irhtemite with a known reference. Irhtemite 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. Irhtemite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Irhtemite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: white, colorless, pinkish.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular crystals, crusts, radial aggregates.

Often confused with

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

mineral

Pharmacosiderite

Mohs 2.5

How to tell apart: Luster reads vitreous on Irhtemite and adamantine on Pharmacosiderite.

How to tell apart: Luster reads vitreous on Irhtemite and vitreous to sub-adamantine on Scorodite.

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Often found alongside irhtemite

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

All properties

Chemical formula: Ca₄Mg(AsO₄)₂(AsO₃OH)₂·4H₂O
Mohs hardness: 3
Density: 3.37 g/cm³
Colors: White Colorless Pinkish
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Tabular Crystals, Crusts, Radial Aggregates
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Hydrothermal Cobalt-nickel-arsenic Veins
Typical price: $50-300 per specimen

Where rockhounds find irhtemite

Classic worldwide localities

Bou Azzer, Morocco

Field-hunting tip

Look in hydrothermal cobalt-nickel-arsenic veins country — that is the host setting where irhtemite typically forms. If you start seeing arsenolite, picropharmacolite, fluckite in float, you are in the right ground. Field specimens usually show a tabular crystals, crusts, radial aggregates habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify irhtemite?+

Mohs hardness is 3. It typically shows a vitreous luster. The streak is white. Common colors include white, colorless, pinkish.

Where is irhtemite found?+

Notable localities include Bou Azzer, Morocco.

How much is irhtemite worth?+

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

Is irhtemite safe to handle?+

It contains toxic constituents. Contains arsenic, a toxic element. Wash hands thoroughly after handling and avoid inhaling dust or powder. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like irhtemite?+

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

What minerals are found with irhtemite?+

Irhtemite commonly co-occurs with Arsenolite, Picropharmacolite, Fluckite, Erythrite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does irhtemite form in?+

Irhtemite typically forms in hydrothermal cobalt-nickel-arsenic veins. Working float back to the host body is the standard way to chase a fresh occurrence.

What is irhtemite used for?+

Irhtemite is used in collector.

Find irhtemite on the map

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