Ferrisurite is a rare phyllosilicate mineral that typically appears as soft, fibrous, or earthy yellow masses within hydrothermal alteration zones. It is often found associated with lead-bearing mineral deposits and is primarily sought after by advanced collectors of rare species due to its scarcity.

Hardness

2-3

Mohs

Luster

Earthy

Streak

Yellow

Transparency

Opaque

mineralrare

Ferrisurite

Hardness: 2-3
Luster: Earthy
Streak: Yellow
Transparency: Opaque

Is this ferrisurite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch ferrisurite with a known reference. Ferrisurite sits at Mohs 2-3, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Ferrisurite leaves a yellow streak.
3
Read the luster
Hold the specimen under a strong light. Ferrisurite typically shows a earthy luster.
4
Match the color range
Compare against the expected color range: yellow, golden-yellow, brownish-yellow.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: fibrous aggregates.

Often confused with

Ferrisurite vs. its common look-alikes, and how to tell them apart in the field.

mineral

Nontronite

Mohs 1.5-2

How to tell apart: Luster reads earthy on Ferrisurite and dull on Nontronite.

How to tell apart: Luster reads earthy on Ferrisurite and vitreous on Jarosite.

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Often found alongside ferrisurite

Minerals reported to co-occur with ferrisurite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: (Fe³⁺,Pb,Ca)₂(Si,Al)₄O₁₀(OH)₂·nH₂O
Mohs hardness: 2-3
Density: 2.8 g/cm³
Colors: Yellow Golden-yellow Brownish-yellow
Streak: Yellow
Luster: Earthy
Transparency: Opaque
Crystal system: Monoclinic
Crystal habit: Fibrous Aggregates
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Hydrothermal Alteration Zones
Typical price: $20-100 per specimen

Where rockhounds find ferrisurite

Classic worldwide localities

Tolfa Mountains, Italy
Arizona, USA
Nevada, USA

Field-hunting tip

Look in hydrothermal alteration zones country, the host setting where ferrisurite typically forms. If you start seeing jarosite, goethite, quartz in float, you are in the right ground. Field specimens usually show a fibrous aggregates habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify ferrisurite?+

Mohs hardness is 2-3. It typically shows a earthy luster. The streak is yellow. Common colors include yellow, golden-yellow, brownish-yellow.

Where is ferrisurite found?+

Notable localities include Tolfa Mountains, Italy; Arizona, USA; Nevada, USA.

How much is ferrisurite worth?+

Typical asking prices fall in the range of $20-100 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

Is ferrisurite safe to handle?+

It contains toxic constituents. Contains lead, so handle with care, avoid creating dust, and wash hands thoroughly after handling. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like ferrisurite?+

Ferrisurite is most often confused with Nontronite, Jarosite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with ferrisurite?+

Ferrisurite commonly co-occurs with Jarosite, Goethite, Quartz. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does ferrisurite form in?+

Ferrisurite typically forms in hydrothermal alteration zones. Working float back to the host body is the standard way to chase a fresh occurrence.

What is ferrisurite used for?+

Ferrisurite is used in collector.

Find ferrisurite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.