Fuenzalidaite is a rare potassium sodium magnesium sulfate, typically colorless to bright yellow. It is a rare constituent of nitrate ores. Associated minerals include nitratine, halite and probertite. It was first described from one km south of Oficina Santa Luisa, Antofagasta, Chile.

Hardness

2-3

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrareEuclase-Vonsenite Group family

Fuenzalidaite

Hardness: 2-3
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this fuenzalidaite?

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 fuenzalidaite with a known reference. Fuenzalidaite 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. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: white, pale yellow.
5
Look at form & habit
Crystal system: trigonal. Typical habit: platy.

Often confused with

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

mineral

Jarosite

Mohs 2.5-3.5

How to tell apart: Streak differs, so Fuenzalidaite leaves white, Jarosite leaves pale yellow; luster reads vitreous on Fuenzalidaite and subadamantine to vitreous, resinous on fractures on Jarosite.

Often found alongside fuenzalidaite

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

All properties

Chemical formula: K₃Na₅Mg₅(IO₃)₆(SO₄)₆·6H₂O
Mohs hardness: 2-3
Density: 3.31 g/cm³
Colors: White Pale yellow
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Trigonal
Crystal habit: Platy
Cleavage: On {1120}, likely, visible on SEM images
Rarity: Rare
Uses: Collector
Host rock: A rare constituent of nitrate ores

Where rockhounds find fuenzalidaite

Classic worldwide localities

A former nitrate mine about 1 km south of the former plant site of Oficina Santa Luisa, Chile (type locality)

Field-hunting tip

Where it forms: A rare constituent of nitrate ores. If you start seeing nitratine, halite, probertite in float, you are in the right ground. Typical habit: platy. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify fuenzalidaite?+

Mohs hardness is 2-3. Luster: vitreous. The streak is white. Common colors include white, pale yellow.

Where is fuenzalidaite found?+

Notable localities include A former nitrate mine about 1 km south of the former plant site of Oficina Santa Luisa, Chile (type locality).

What rocks look like fuenzalidaite?+

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

What minerals are found with fuenzalidaite?+

Fuenzalidaite commonly co-occurs with Nitratine, Halite, Probertite, Darapskite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does fuenzalidaite form in?+

Where it forms: A rare constituent of nitrate ores. Working float back to the host body is the standard way to chase a fresh occurrence.

What is fuenzalidaite used for?+

Fuenzalidaite is used in collector.

Find fuenzalidaite on the map

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