Mckinstryite is a rare silver-copper sulfide that is typically found in low-temperature hydrothermal veins. It is most easily identified by its characteristic iron-black to steel-gray color and metallic luster, though it is often indistinguishable from other silver sulfides without microscopic or chemical analysis.
Is this mckinstryite?
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 mckinstryite with a known reference. Mckinstryite sits at Mohs 1.5-2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: dark steel-gray.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: dark gray, black, steel gray.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: aggregates, granular, microscopic crystals.
Often confused with
Mckinstryite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Mckinstryite leaves dark steel-gray, Acanthite leaves black.
How to tell apart: Streak differs, so Mckinstryite leaves dark steel-gray, Stromeyerite leaves steel-gray.
How to tell apart: Streak differs, so Mckinstryite leaves dark steel-gray, Jalpaite leaves black.
Often found alongside mckinstryite
Minerals reported to co-occur with mckinstryite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Ag,Cu)₂S
- Mohs hardness
- 1.5-2.5
- Density
- 6.61 g/cm³
- Colors
- Streak
- Dark steel-gray
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Aggregates, granular, microscopic crystals
- Cleavage
- One, poorly developed
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Of hydrothermal or supergene origin; probably formed below 94.4°C, the upper stability limit for mckinstryite
Where rockhounds find mckinstryite
Classic worldwide localities
- Central mine, Georgetown district, Clear Creek Co., and the Bulldog Mountain mine, Creede district, Mineral Co., Colorado, USA
- Mogollon, Catron Co., New Mexico, USA
- Homestake deposit, near Cooke City, Park Co., Montana, USA
- Foster mine, Coleman Township, about two km southeast of Cobalt, Ontario (type locality), and from the Echo Bay mine, Great Bear Lake, Northwest Territories, Canada
- Jalpa, Zacatecas, Mexico
- Godejord, Grong area, and in the Bleikvassli Zn–Pb–Cu deposit, Nordland, Norway
Field-hunting tip
Where it forms: Of hydrothermal or supergene origin; probably formed below 94.4°C, the upper stability limit for mckinstryite. If you start seeing silver, arsenopyrite, stromeyerite in float, you are in the right ground. Typical habit: aggregates, granular, microscopic crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify mckinstryite?+
Where is mckinstryite found?+
Is mckinstryite safe to handle?+
What rocks look like mckinstryite?+
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Find mckinstryite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
