Tochilinite is a rare, complex mineral consisting of alternating layers of iron sulfide and magnesium-iron hydroxide. It is typically found in serpentinized ultramafic environments, often appearing as dark, metallic, flexible flakes or thin coatings on other minerals like magnetite.
Is this tochilinite?
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 tochilinite with a known reference. Tochilinite sits at Mohs 1-1.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: black.
- 3Read the lusterHold the specimen under a strong light. Luster: moderately metallic.
- 4Match the color rangeCompare against the expected color range: bronze black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular, cylindrical, radial.
Often confused with
Tochilinite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Mackinawite is the harder of the two (Mohs 2.5 vs. 1-1.5); luster reads moderately metallic on Tochilinite and metallic on Mackinawite.
How to tell apart: Luster reads moderately metallic on Tochilinite and metallic to submetallic on Valleriite.
How to tell apart: Luster reads moderately metallic on Tochilinite and metallic; may be dull, earthy on Graphite.
Often found alongside tochilinite
Minerals reported to co-occur with tochilinite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe₅₊ₓS₆(Mg,Fe)₉(OH)₁₈
- Mohs hardness
- 1-1.5
- Density
- 2.96 g/cm³
- Colors
- Bronze black
- Streak
- Black
- Luster
- Moderately metallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Acicular, cylindrical, radial
- Cleavage
- On {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In sulfide-rich serpentinized ultramafic bodies, where it may be of rock-forming mineral abundance; in some carbonaceous chondrite meteorites
Where rockhounds find tochilinite
Classic worldwide localities
- Grace mine, Morgantown, Berks Co., and the Cornwall open pit, Lebanon Co., Pennsylvania, USA
- Voronezh district, from the Nizhnii Mamon Cu–Ni deposit, Nizhnii Mamon intrusive, 45 km southeast of Pavlovsk (type locality), and in the Staromelovatskii intrusive, Russia
- Mir, Udachnaya, and Obnazhennaya diamond pipes, Sakha, Russia
- Stephen Cross and Maxwell quarries, near Wakefield, and from the Dumont property, near Amos, Quebec, Canada
- Muskox intrusion, Northwest Territories, Canada
- Bancroft, Ontario, Canada
Field-hunting tip
Where it forms: In sulfide-rich serpentinized ultramafic bodies, where it may be of rock-forming mineral abundance; in some carbonaceous chondrite meteorites. If you start seeing troilite, pyrrhotite, sphalerite in float, you are in the right ground. Typical habit: acicular, cylindrical, radial. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify tochilinite?+
Where is tochilinite found?+
What rocks look like tochilinite?+
What minerals are found with tochilinite?+
What kind of rock does tochilinite form in?+
What is tochilinite used for?+
Find tochilinite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
