Charlesite is an uncommon sulfate mineral belonging to the ettringite group, occurring as colorless to pale yellow hexagonal crystals. It is most famous for its occurrence in the zinc mines of Franklin and Sterling Hill, New Jersey, typically found in association with silicate and carbonate minerals.
Is this charlesite?
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 charlesite with a known reference. Charlesite sits at Mohs 2.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Charlesite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Charlesite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, pale yellow.
- 5Look at form & habitCrystal system: trigonal. Typical habit: hexagonal prisms with pyramidal terminations.
Often confused with
Charlesite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside charlesite
Minerals reported to co-occur with charlesite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₆(Si₂O₄(OH)₆)(SO₄)₂·26H₂O
- Mohs hardness
- 2.5
- Density
- 1.79 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Trigonal
- Crystal habit
- Hexagonal Prisms with Pyramidal Terminations
- Cleavage
- Perfect On {10-10}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metamorphosed Zinc Ore Deposits
- Typical price
- $50-300 per specimen depending on size and crystal quality
Where rockhounds find charlesite
Classic worldwide localities
- Franklin Mine, New Jersey, USA
- Sterling Hill Mine, New Jersey, USA
Field-hunting tip
Look in metamorphosed zinc ore deposits country — that is the host setting where charlesite typically forms. If you start seeing grossular, vesuvianite, willemite in float, you are in the right ground. Field specimens usually show a hexagonal prisms with pyramidal terminations habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find charlesite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
