Mcnearite is a rare secondary arsenate mineral typically found as delicate acicular crystals or radial tufts in hydrothermal veins. It is predominantly associated with other arsenic-bearing minerals and is highly prized by collectors for its rarity and crystal structure. Collectors should handle it with care due to its arsenic content.
Is this mcnearite?
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 mcnearite with a known reference. Mcnearite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly.
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: triclinic. Typical habit: fibrous, radial.
Often confused with
Mcnearite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Mcnearite leaves white, Pharmacosiderite leaves yellowish green; luster reads pearly on Mcnearite and adamantine to greasy on Pharmacosiderite.
How to tell apart: Streak differs, so Mcnearite leaves white, Yukonite leaves brownish yellow; luster reads pearly on Mcnearite and vitreous to resinous on Yukonite.
Often found alongside mcnearite
Minerals reported to co-occur with mcnearite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaCa₅(AsO₄)(AsO₃OH)₄·4H₂O
- Mohs hardness
- 2
- Density
- 2.60 g/cm³
- Colors
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent to transparent
- Crystal system
- Triclinic
- Crystal habit
- Fibrous, radial
- Cleavage
- Perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral in the oxidized zone of an arsenic-bearing deposit
Where rockhounds find mcnearite
Classic worldwide localities
- Sainte-Marie-aux-Mines, Haut-Rhin, France
Field-hunting tip
Where it forms: A secondary mineral in the oxidized zone of an arsenic-bearing deposit. If you start seeing picropharmacolite, pharmacolite, guérinite in float, you are in the right ground. Typical habit: fibrous, radial. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify mcnearite?+
Where is mcnearite found?+
Is mcnearite safe to handle?+
What rocks look like mcnearite?+
What minerals are found with mcnearite?+
What kind of rock does mcnearite form in?+
What is mcnearite used for?+
Find mcnearite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
