Humberstonite is a rare sulfate-nitrate mineral typically found in the extremely arid evaporite deposits of the Atacama Desert. Collectors usually find it as small, colorless to white tabular crystals or as granular masses associated with other nitrate minerals.

Hardness

~2.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Humberstonite

Hardness: ~2.5
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this humberstonite?

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 humberstonite with a known reference. Humberstonite 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. 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: colorless.
5
Look at form & habit
Crystal system: trigonal. Typical habit: tabular crystals, massive.

Often confused with

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

Often found alongside humberstonite

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

All properties

Chemical formula: K₃Na₇Mg₂(SO₄)₆(NO₃)₂·6H₂O
Mohs hardness: ~2.5
Density: 2.252 g/cm³
Colors: Colorless
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Trigonal
Crystal habit: Tabular crystals, massive
Cleavage: Perfect on {0001}
Rarity: Rare
Uses: Collector
Host rock: Formed by repeated natural leaching of nitrate ore with reprecipitation in irregular pods above the local regolith

Where rockhounds find humberstonite

Classic worldwide localities

Humberstone Nitrate Works, Tarapacá, Chile
Salar de Atacama, Chile

Field-hunting tip

Where it forms: Formed by repeated natural leaching of nitrate ore with reprecipitation in irregular pods above the local regolith. If you start seeing blödite, nitratine, kieserite in float, you are in the right ground. Typical habit: tabular crystals, massive. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify humberstonite?+

Mohs hardness is ~2.5. Luster: vitreous. The streak is white. Common colors include colorless.

Where is humberstonite found?+

Notable localities include Humberstone Nitrate Works, Tarapacá, Chile; Salar de Atacama, Chile.

What rocks look like humberstonite?+

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

What minerals are found with humberstonite?+

Humberstonite commonly co-occurs with Blödite, Nitratine, Kieserite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does humberstonite form in?+

Where it forms: Formed by repeated natural leaching of nitrate ore with reprecipitation in irregular pods above the local regolith. Working float back to the host body is the standard way to chase a fresh occurrence.

What is humberstonite used for?+

Humberstonite is used in collector.

Find humberstonite on the map

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