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

Silky

Streak

White

Transparency

Transparent

mineralrare

Irhtemite

Hardness: 3
Luster: Silky
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. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: silky.
4
Match the color range
Compare against the expected color range: white, colorless, pale rose, pink.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: spherical.

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: Streak differs, so Irhtemite leaves white, Pharmacosiderite leaves yellowish green; luster reads silky on Irhtemite and adamantine to greasy on Pharmacosiderite.

How to tell apart: Streak differs, so Irhtemite leaves white, Scorodite leaves greenish white; luster reads silky on Irhtemite and vitreous to subadamantine, subresinous on Scorodite.

Compare →

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: 3.09 g/cm³
Colors: White ColorlessPale rosePink
Streak: White
Luster: Silky
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Spherical
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Probably a dehydration product of picropharmacolite in hydrothermal ore deposits

Where rockhounds find irhtemite

Classic worldwide localities

Irhtem (Ightem) mine, Bou Azzer district, Anti-Atlas Mountains, Morocco
Bauhaus district, Richelsdorf Mountains, Hesse, Germany

Field-hunting tip

Where it forms: Probably a dehydration product of picropharmacolite in hydrothermal ore deposits. If you start seeing sainfeldite, erythrite in float, you are in the right ground. Typical habit: spherical. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify irhtemite?+

Mohs hardness is 3. Luster: silky. The streak is white. Common colors include white, colorless, pale rose, pink.

Where is irhtemite found?+

Notable localities include Irhtem (Ightem) mine, Bou Azzer district, Anti-Atlas Mountains, Morocco; Bauhaus district, Richelsdorf Mountains, Hesse, Germany.

Is irhtemite safe to handle?+

Irhtemite contains arsenic and calls for real care. Contains arsenic, a toxic element. Wash hands thoroughly after handling and avoid inhaling dust or powder.

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 Sainfeldite, Erythrite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does irhtemite form in?+

Where it forms: Probably a dehydration product of picropharmacolite in hydrothermal ore deposits. 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.