Arsenocrandallite is a rare phosphate-arsenate mineral belonging to the crandallite group, typically found in the oxidized zones of arsenic-rich ore deposits. It usually forms as small, inconspicuous crusts or fine-grained aggregates that require careful identification through X-ray diffraction or microprobe analysis. Collectors seek it out as a specialized species from specific localities such as the Reaphook Hill occurrence in Australia.

Hardness

~5.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Semitransparent

mineralrareCrandallite Group family

Arsenocrandallite

Hardness: ~5.5
Luster: Vitreous
Streak: White
Transparency: Semitransparent

Is this arsenocrandallite?

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 arsenocrandallite with a known reference. Arsenocrandallite sits at Mohs ~5.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: blue green, blue.
5
Look at form & habit
Crystal system: trigonal. Typical habit: microcrystalline aggregates, crusts, rhombohedral crystals.

Often confused with

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

Often found alongside arsenocrandallite

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

All properties

Chemical formula: CaAl₃(AsO₄)(AsO₃OH)(OH)₆
Mohs hardness: ~5.5
Density: 3.25 g/cm³
Colors: Blue green Blue
Streak: White
Luster: Vitreous
Transparency: Semitransparent
Crystal system: Trigonal
Crystal habit: Microcrystalline aggregates, crusts, rhombohedral crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: A secondary mineral on specimens from a mine dump (Neubulach, Germany)

Where rockhounds find arsenocrandallite

Classic worldwide localities

Centennial Eureka mine, Tintic district, Juab Co., Utah, USA
Neubulach, and in the Clara mine, near Oberwolfach, Black Forest, Germany

Field-hunting tip

Where it forms: A secondary mineral on specimens from a mine dump (Neubulach, Germany). If you start seeing brochantite, chalcophyllite, parnauite in float, you are in the right ground. Typical habit: microcrystalline aggregates, crusts, rhombohedral crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify arsenocrandallite?+

Mohs hardness is ~5.5. Luster: vitreous. The streak is white. Common colors include blue green, blue.

Where is arsenocrandallite found?+

Notable localities include Centennial Eureka mine, Tintic district, Juab Co., Utah, USA; Neubulach, and in the Clara mine, near Oberwolfach, Black Forest, Germany.

Is arsenocrandallite safe to handle?+

Arsenocrandallite contains arsenic and calls for real care. Contains arsenic, which is toxic. Wash hands thoroughly after handling and avoid inhaling dust.

What rocks look like arsenocrandallite?+

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

What minerals are found with arsenocrandallite?+

Arsenocrandallite commonly co-occurs with Brochantite, Chalcophyllite, Parnauite, Barian pharmacosiderite, Bulachite, Arseniosiderite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does arsenocrandallite form in?+

Where it forms: A secondary mineral on specimens from a mine dump (Neubulach, Germany). Working float back to the host body is the standard way to chase a fresh occurrence.

What is arsenocrandallite used for?+

Arsenocrandallite is used in collector.

Find arsenocrandallite on the map

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