Franklinite is a distinctive black, metallic mineral primarily known for its occurrences in the unique ore bodies of Franklin and Sterling Hill, New Jersey. It is strongly magnetic and typically found as well-formed octahedral crystals embedded in a fluorescent matrix of calcite and willemite.
Is this franklinite?
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 franklinite with a known reference. Franklinite sits at Mohs 5.5-6.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Franklinite leaves a reddish-brown streak.
- 3Read the lusterHold the specimen under a strong light. Franklinite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: black, brownish-black.
- 5Look at form & habitCrystal system: cubic. Typical habit: octahedral crystals, massive, granular.
Often confused with
Franklinite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Franklinite leaves reddish-brown, Magnetite leaves black.
How to tell apart: Streak differs, so Franklinite leaves reddish-brown, Chromite leaves dark brown; luster reads metallic on Franklinite and submetallic on Chromite.
How to tell apart: Streak differs, so Franklinite leaves reddish-brown, Hausmannite leaves brownish-red; luster reads metallic on Franklinite and submetallic on Hausmannite.
Often found alongside franklinite
Minerals reported to co-occur with franklinite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Zn,Mn²⁺,Fe²⁺)(Fe³⁺,Mn³⁺)₂O₄
- Mohs hardness
- 5.5-6.5
- Density
- 5.0-5.3 g/cm³
- Colors
- Streak
- Reddish-brown
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Octahedral Crystals, Massive, Granular
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector, Ore of Zinc
- Host rock
- Metamorphosed Zinc Ore Deposits
- Typical price
- $10-100 per specimen
Where rockhounds find franklinite
2 mapped spotsClassic worldwide localities
- Franklin, New Jersey, USA
- Sterling Hill, New Jersey, USA
- Langban, Sweden
Field-hunting tip
Look in metamorphosed zinc ore deposits country, the host setting where franklinite typically forms. If you start seeing willemite, calcite, zincite in float, you are in the right ground. Field specimens usually show a octahedral crystals, massive, granular habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in New Jersey. Start trip planning there.
Common questions
How do you identify franklinite?+
Where is franklinite found?+
Can I find franklinite in the United States?+
How much is franklinite worth?+
What rocks look like franklinite?+
What minerals are found with franklinite?+
What kind of rock does franklinite form in?+
What is franklinite used for?+
Find franklinite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
