Gratonite is a rare lead arsenic sulfide mineral typically found as small, lead-gray prismatic crystals. It is almost exclusively associated with the lead-zinc deposits of the Cerro de Pasco district in Peru. Due to its high lead and arsenic content, collectors should exercise caution and handle specimens with care.
Is this gratonite?
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 gratonite with a known reference. Gratonite 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. Gratonite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Gratonite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: lead-gray, dark gray.
- 5Look at form & habitCrystal system: trigonal. Typical habit: prismatic crystals, acicular, granular.
Often confused with
Gratonite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Gratonite leaves black, Galena leaves lead-gray.
How to tell apart: Streak differs — Gratonite leaves black, Boulangerite leaves brownish-gray.
How to tell apart: Streak differs — Gratonite leaves black, Jamesonite leaves gray-black.
Often found alongside gratonite
Minerals reported to co-occur with gratonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pb₉As₄S₁₅
- Mohs hardness
- 2.5
- Density
- 6.25 g/cm³
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Prismatic Crystals, Acicular, Granular
- Cleavage
- Poor
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Sulfide Veins
- Typical price
- $50-300 per thumbnail or small specimen
Where rockhounds find gratonite
Classic worldwide localities
- Excelsior Mine, Cerro de Pasco, Peru
Field-hunting tip
Look in hydrothermal sulfide veins country — that is the host setting where gratonite typically forms. If you start seeing galena, pyrite, sphalerite in float, you are in the right ground. Field specimens usually show a prismatic crystals, acicular, granular habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify gratonite?+
Where is gratonite found?+
How much is gratonite worth?+
Is gratonite safe to handle?+
What rocks look like gratonite?+
What minerals are found with gratonite?+
What kind of rock does gratonite form in?+
What is gratonite used for?+
Find gratonite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
