Ardennite-(As) is a rare silicate mineral primarily found in manganese-rich metamorphic deposits. It typically forms elongated, prismatic crystals that often appear in radiated sprays or fibrous masses with a distinctive yellowish-brown to reddish-brown coloration.

Hardness

6-7

Mohs

Luster

Vitreous

Streak

White

Transparency

Translucent

mineralrareArdennite Group family

Ardennite-(As)

Hardness: 6-7
Luster: Vitreous
Streak: White
Transparency: Translucent

Is this ardennite-(as)?

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 ardennite-(as) with a known reference. Ardennite-(As) sits at Mohs 6-7 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Ardennite-(As) leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Ardennite-(As) typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: yellow-brown, brown, red-brown.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: prismatic crystals, radial aggregates, fibrous.

Often confused with

Ardennite-(As) vs. its common look-alikes — and how to tell them apart in the field.

Often found alongside ardennite-(as)

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

All properties

Chemical formula: (Mn²⁺,Ca,Mg)₄(Al,Fe³⁺)₆(SiO₄)₂(Si₃O₁₀)(AsO₄)(OH)₆
Mohs hardness: 6-7
Density: 3.6-3.7 g/cm³
Colors: Yellow-brown Brown Red-brown
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Orthorhombic
Crystal habit: Prismatic Crystals, Radial Aggregates, Fibrous
Cleavage: Good On {110}
Rarity: Rare
Uses: Collector
Host rock: Manganese-rich Metamorphic Rocks
Typical price: $50-500 thumbnail, $200-1500 cabinet

Where rockhounds find ardennite-(as)

Classic worldwide localities

Ardenne, Belgium
Saint-Marcel, Italy
Alps, Switzerland
Japan

Field-hunting tip

Look in manganese-rich metamorphic rocks country — that is the host setting where ardennite-(as) typically forms. If you start seeing quartz, spessartine, braunite in float, you are in the right ground. Field specimens usually show a prismatic crystals, radial aggregates, fibrous habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify ardennite-(as)?+

Mohs hardness is 6-7. It typically shows a vitreous luster. The streak is white. Common colors include yellow-brown, brown, red-brown.

Where is ardennite-(as) found?+

Notable localities include Ardenne, Belgium; Saint-Marcel, Italy; Alps, Switzerland; Japan.

How much is ardennite-(as) worth?+

Typical asking prices fall in the range of $50-500 thumbnail, $200-1500 cabinet. Quality, size, and provenance can move individual specimens well outside that range.

Is ardennite-(as) safe to handle?+

It contains toxic constituents. Contains arsenic. Wash hands thoroughly after handling and avoid creating dust when breaking specimens. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like ardennite-(as)?+

Ardennite-(As) is most often confused with Epidote. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with ardennite-(as)?+

Ardennite-(As) commonly co-occurs with Quartz, Spessartine, Braunite, Hematite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does ardennite-(as) form in?+

Ardennite-(As) typically forms in manganese-rich metamorphic rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is ardennite-(as) used for?+

Ardennite-(As) is used in collector.

Find ardennite-(as) on the map

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