Wallkilldellite is a rare arsenate mineral that occurs as distinct platy crystals or thin crusts, typically displaying a rich reddish color. It is primarily found in the complex manganese-zinc ore deposits of the Franklin-Sterling Hill district in New Jersey. Due to its rarity and specific chemical composition, it is highly sought after by advanced systematic mineral collectors.
Is this wallkilldellite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch wallkilldellite with a known reference. Wallkilldellite sits at Mohs ~3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale orange.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous on cleavage surfaces; slightly resinous on fracture surfaces.
- 4Match the color rangeCompare against the expected color range: dark red.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: platy crystals, crusts.
Often confused with
Wallkilldellite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Allactite is the harder of the two (Mohs 4.5 vs. ~3); streak differs, so Wallkilldellite leaves pale orange, Allactite leaves gray to faint brown.
How to tell apart: Flinkite is the harder of the two (Mohs 4.5 vs. ~3); streak differs, so Wallkilldellite leaves pale orange, Flinkite leaves light brown.
Often found alongside wallkilldellite
Minerals reported to co-occur with wallkilldellite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₄Mn₆(AsO₄)₄(OH)₈·18H₂O
- Mohs hardness
- ~3
- Density
- 2.85 g/cm³
- Colors
- Streak
- Pale orange
- Luster
- Vitreous on cleavage surfaces; slightly resinous on fracture surfaces
- Transparency
- Semitransparent
- Crystal system
- Hexagonal
- Crystal habit
- Platy crystals, crusts
- Cleavage
- Perfect on {0001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Extremely rare in massive granular franklinite-willemite ore from a metamorphosed stratiform zinc orebody (Sterling Hill)
Where rockhounds find wallkilldellite
Classic worldwide localities
- Sterling Hill, Ogdensburg, Sussex Co., New Jersey, USA
- Monte Nero mine, Rocchetta Vara, La Spezia, Liguria, Italy
Field-hunting tip
Where it forms: Extremely rare in massive granular franklinite-willemite ore from a metamorphosed stratiform zinc orebody (Sterling Hill). If you start seeing manganoan cuprian adamite, franklinite, willemite in float, you are in the right ground. Typical habit: platy crystals, crusts. Train your eye for that shape before scanning the outcrop.
Common questions
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Find wallkilldellite on the map
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