Wallkilldellite-(Fe) is a rare arsenate mineral characterized by its reddish-brown platy crystals and radial habits. It is primarily found in the metamorphosed zinc ore deposits of the Sterling Hill Mine, where it occurs as a late-stage secondary mineral. Collectors value it for its limited occurrence and relationship to other rare Franklin-area arsenates.

Hardness

2-3

Mohs

Luster

Vitreous on cleavage surfaces; slightly resinous on fracture surfaces

Streak

Light brown

Transparency

Translucent

mineralrareWallkilldellite Group family

Wallkilldellite-(Fe)

Hardness: 2-3
Luster: Vitreous on cleavage surfaces; slightly resinous on fracture surfaces
Streak: Light brown
Transparency: Translucent

Is this wallkilldellite-(fe)?

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 wallkilldellite-(fe) with a known reference. Wallkilldellite-(Fe) sits at Mohs 2-3, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: light brown.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous on cleavage surfaces; slightly resinous on fracture surfaces.
4
Match the color range
Compare against the expected color range: brownish yellow.
5
Look at form & habit
Crystal system: hexagonal. Typical habit: microscopic crystals, spherical.

Often confused with

Wallkilldellite-(Fe) vs. its common look-alikes, and how to tell them apart in the field.

How to tell apart: Streak differs, so Wallkilldellite-(Fe) leaves light brown, Wallkilldellite leaves pale orange.

How to tell apart: Streak differs, so Wallkilldellite-(Fe) leaves light brown, Chlorophoenicite leaves white.

Compare →

Often found alongside wallkilldellite-(fe)

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

All properties

Chemical formula: Ca₂Fe₃(AsO₄)₂(OH)₄·9H₂O
Mohs hardness: 2-3
Density: 3.0 g/cm³
Colors: Brownish yellow
Streak: Light brown
Luster: Vitreous on cleavage surfaces; slightly resinous on fracture surfaces
Transparency: Translucent
Crystal system: Hexagonal
Crystal habit: Microscopic crystals, spherical
Cleavage: Perfect on {0001}
Rarity: Rare
Uses: Collector
Host rock: Secondary in the oxidation zone of copper arsenide deposits

Where rockhounds find wallkilldellite-(fe)

Classic worldwide localities

Roua mine, Alpes-Maritimes, France and the Uriya deposit, Kura mine, Saiki City, Oita Prefecture, Japan

Field-hunting tip

Where it forms: Secondary in the oxidation zone of copper arsenide deposits. If you start seeing cuprite, algodonite, domeykite in float, you are in the right ground. Typical habit: microscopic crystals, spherical. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify wallkilldellite-(fe)?+

Mohs hardness is 2-3. Luster: vitreous on cleavage surfaces; slightly resinous on fracture surfaces. The streak is light brown. Common colors include brownish yellow.

Where is wallkilldellite-(fe) found?+

Notable localities include Roua mine, Alpes-Maritimes, France and the Uriya deposit, Kura mine, Saiki City, Oita Prefecture, Japan.

Is wallkilldellite-(fe) safe to handle?+

Wallkilldellite-(Fe) contains arsenic and calls for real care. Contains arsenic, which is toxic. Handle with care, avoid creating dust, and wash hands thoroughly after handling.

What rocks look like wallkilldellite-(fe)?+

Wallkilldellite-(Fe) is most often confused with Wallkilldellite, Chlorophoenicite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with wallkilldellite-(fe)?+

Wallkilldellite-(Fe) commonly co-occurs with Cuprite, Algodonite, Domeykite, Koutekite, Olivenite, Kolfanite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does wallkilldellite-(fe) form in?+

Where it forms: Secondary in the oxidation zone of copper arsenide deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is wallkilldellite-(fe) used for?+

Wallkilldellite-(Fe) is used in collector.

Find wallkilldellite-(fe) on the map

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