Hendricksite is a rare zinc-bearing member of the mica group, typically identified by its dark, bronzy, micaceous platy crystals. It is primarily found within the unique mineral environment of the Sterling Hill mine in New Jersey. Collectors should look for its distinctive pearly luster and perfect basal cleavage characteristic of the mica family.
Is this hendricksite?
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 hendricksite with a known reference. Hendricksite sits at Mohs 2.5-3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: red brown.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly.
- 4Match the color rangeCompare against the expected color range: copper brown, red, reddish black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: aggregates, euhedral crystals, foliated.
Often confused with
Hendricksite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Hendricksite leaves red brown, Biotite leaves white; luster reads pearly on Hendricksite and splendent to submetallic, vitreous, pearly on cleavage on Biotite.
How to tell apart: Streak differs, so Hendricksite leaves red brown, Phlogopite leaves white.
Often found alongside hendricksite
Minerals reported to co-occur with hendricksite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KZn₃(Si₃Al)O₁₀(OH)₂
- Mohs hardness
- 2.5-3
- Density
- 2.86-3.43 g/cm³
- Colors
- Streak
- Red brown
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Aggregates, euhedral crystals, foliated
- Cleavage
- {001}, perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Restricted to irregular lens- or sheetlike skarn bodies in a metamorphosed stratiform zinc deposit
Where rockhounds find hendricksite
Classic worldwide localities
- Franklin, Sussex Co., New Jersey, USA
Field-hunting tip
Where it forms: Restricted to irregular lens- or sheetlike skarn bodies in a metamorphosed stratiform zinc deposit. If you start seeing andradite, rhodonite, calcite in float, you are in the right ground. Typical habit: aggregates, euhedral crystals, foliated. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify hendricksite?+
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What rocks look like hendricksite?+
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Find hendricksite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
