Siderotil is a secondary sulfate mineral that typically forms as an efflorescent crust or fibrous coating on rock surfaces in mine workings. It is chemically unstable and dehydration-prone, often requiring careful storage to prevent it from turning into a white powder as it alters to rozenite.

Hardness

2.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Translucent

mineraluncommonMelanterite Group family

Siderotil

Hardness: 2.5
Luster: Vitreous
Streak: White
Transparency: Translucent

Is this siderotil?

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 siderotil with a known reference. Siderotil sits at Mohs 2.5 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Siderotil leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Siderotil typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: white, pale blue, pale green.
5
Look at form & habit
Crystal system: triclinic. Typical habit: fibrous, efflorescent crusts, powdery coatings.

Often confused with

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

Often found alongside siderotil

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

All properties

Chemical formula: (Fe,Cu)SO₄·5H₂O
Mohs hardness: 2.5
Density: 1.97 g/cm³
Colors: White Pale Blue Pale Green
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Triclinic
Crystal habit: Fibrous, Efflorescent Crusts, Powdery Coatings
Cleavage: None
Rarity: Uncommon
Uses: Collector
Host rock: Oxidized Zones of Sulfide Ore Deposits
Typical price: $10-60 for small specimens

Where rockhounds find siderotil

Classic worldwide localities

Rio Tinto, Spain
Bisbee, Arizona, USA
Chuquicamata, Chile
Rammelsberg, Germany

Field-hunting tip

Look in oxidized zones of sulfide ore deposits country — that is the host setting where siderotil typically forms. If you start seeing melanterite, chalcanthite, pyrite in float, you are in the right ground. Field specimens usually show a fibrous, efflorescent crusts, powdery coatings habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify siderotil?+

Mohs hardness is 2.5. It typically shows a vitreous luster. The streak is white. Common colors include white, pale blue, pale green.

Where is siderotil found?+

Notable localities include Rio Tinto, Spain; Bisbee, Arizona, USA; Chuquicamata, Chile; Rammelsberg, Germany.

How much is siderotil worth?+

Typical asking prices fall in the range of $10-60 for small specimens. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like siderotil?+

Siderotil is most often confused with Melanterite, Chalcanthite, Rozenite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with siderotil?+

Siderotil commonly co-occurs with Melanterite, Chalcanthite, Pyrite, Copiapite, Jarosite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does siderotil form in?+

Siderotil typically forms in oxidized zones of sulfide ore deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is siderotil used for?+

Siderotil is used in collector.

Find siderotil on the map

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