Sideronatrite is a rare hydrated sodium iron sulfate that typically forms as bright yellow fibrous or crusty aggregates. It is most commonly found in the extremely arid environments of the Atacama Desert in Chile, where it results from the weathering of iron sulfides.

Hardness

1.5-2.5

Mohs

Luster

Vitreous

Streak

Pale yellow

Transparency

Semitransparent

mineralrare

Sideronatrite

Hardness: 1.5-2.5
Luster: Vitreous
Streak: Pale yellow
Transparency: Semitransparent

Is this sideronatrite?

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 sideronatrite with a known reference. Sideronatrite sits at Mohs 1.5-2.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: pale yellow.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: yellow, yellow brown, pale orange.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: fibrous, massive, nodular.

Often confused with

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

mineral

Copiapite

Mohs 2.5-3

How to tell apart: Luster reads vitreous on Sideronatrite and pearly on {010} on Copiapite.

How to tell apart: Streak differs, so Sideronatrite leaves pale yellow, Amarantite leaves lemon-yellow.

Compare →

Often found alongside sideronatrite

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

All properties

Chemical formula: Na₂Fe(SO₄)₂(OH)·3H₂O
Mohs hardness: 1.5-2.5
Density: 2.22-2.35 g/cm³
Colors: Yellow Yellow brownPale orange
Streak: Pale yellow
Luster: Vitreous
Transparency: Semitransparent
Crystal system: Orthorhombic
Crystal habit: Fibrous, massive, nodular
Cleavage: On {010}, perfect; on {100}, fair
Rarity: Rare
Uses: Collector
Host rock: An uncommon secondary mineral in the oxidized zone of iron-rich deposits in very arid climates, may be post-mine

Where rockhounds find sideronatrite

Classic worldwide localities

Hot Springs Point sulfur mine, Crescent Valley, Eureka Co., Nevada, USA
San Simon mine, Huantajaya, Tarapacá, Chile
Compania mine, Sierra Gorda district, southwest of Calama, and at Chuquicamata, Antofagasta, Chile
Potosí, Bolivia
Santa Bárbara sulfur mine, El Palmar district, Jujuy Province, Argentina
Urus Plateau, Cheleken Peninsula, Caspian Sea, Turkmenistan

Field-hunting tip

Where it forms: An uncommon secondary mineral in the oxidized zone of iron-rich deposits in very arid climates, may be post-mine. If you start seeing metasideronatrite, ferrinatrite, copiapite in float, you are in the right ground. Typical habit: fibrous, massive, nodular. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify sideronatrite?+

Mohs hardness is 1.5-2.5. Luster: vitreous. The streak is pale yellow. Common colors include yellow, yellow brown, pale orange.

Where is sideronatrite found?+

Notable localities include Hot Springs Point sulfur mine, Crescent Valley, Eureka Co., Nevada, USA; San Simon mine, Huantajaya, Tarapacá, Chile; Compania mine, Sierra Gorda district, southwest of Calama, and at Chuquicamata, Antofagasta, Chile; Potosí, Bolivia; Santa Bárbara sulfur mine, El Palmar district, Jujuy Province, Argentina.

What rocks look like sideronatrite?+

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

What minerals are found with sideronatrite?+

Sideronatrite commonly co-occurs with Metasideronatrite, Ferrinatrite, Copiapite, Voltaite, Melanterite, Halotrichite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does sideronatrite form in?+

Where it forms: An uncommon secondary mineral in the oxidized zone of iron-rich deposits in very arid climates, may be post-mine. Working float back to the host body is the standard way to chase a fresh occurrence.

What is sideronatrite used for?+

Sideronatrite is used in collector.

Find sideronatrite on the map

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