Geocronite is a rare lead-arsenic sulfosalt often found in hydrothermal lead-zinc deposits. It typically presents as metallic lead-gray massive or granular masses, making it visually similar to galena but distinguishable by its specific chemical associations and rarity.
Is this geocronite?
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 geocronite with a known reference. Geocronite 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. Streak: pale lead-gray to grayish blue.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: blue gray, gray, silver white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: massive.
Often confused with
Geocronite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Geocronite leaves pale lead-gray to grayish blue, Galena leaves lead-gray.
How to tell apart: Streak differs, so Geocronite leaves pale lead-gray to grayish blue, Bournonite leaves steel-gray to iron-black; luster reads metallic on Geocronite and brilliant to dull on Bournonite.
How to tell apart: Streak differs, so Geocronite leaves pale lead-gray to grayish blue, Jamesonite leaves black. grayish.
Often found alongside geocronite
Minerals reported to co-occur with geocronite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pb₁₄Sb₆S₂₃
- Mohs hardness
- 2.5
- Density
- 6.46 g/cm³
- Streak
- Pale lead-gray to grayish blue
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Massive
- Cleavage
- Distinct on {011}
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- In hydrothermal veins with sulfides and other sulfosalt minerals
Where rockhounds find geocronite
Classic worldwide localities
- Silver King mine, Park City district, Summit Co., Utah, USA
- Tintic district, Juab Co., Utah, USA
- Darwin, Inyo Co., California, USA
- Inexco #1 mine, Jamestown, Boulder Co., Colorado, USA
- Kilbricken mine, Co. Clare, and at Silvermines, Co. Tipperary, Ireland
- Bournac, Montagne Noire, Finistère, France
Field-hunting tip
Where it forms: In hydrothermal veins with sulfides and other sulfosalt minerals. If you start seeing galena, pyrite, tetrahedrite in float, you are in the right ground. Typical habit: massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify geocronite?+
Where is geocronite found?+
Is geocronite safe to handle?+
What rocks look like geocronite?+
What minerals are found with geocronite?+
What kind of rock does geocronite form in?+
What is geocronite used for?+
Find geocronite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
