Alfredstelznerite is an extremely rare calcium borate mineral that forms as distinct prismatic crystals within evaporite environments. It is primarily known from its type locality in Argentina, where it is found associated with other borate minerals like ulexite and borax.

Hardness

Mohs

Luster

Vitreous; silky in aggregates

Streak

White

Transparency

Transparent, translucent on dehydration

mineralrare

Alfredstelznerite

Hardness: 2
Luster: Vitreous; silky in aggregates
Streak: White
Transparency: Transparent, translucent on dehydration

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Is this alfredstelznerite?

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 alfredstelznerite with a known reference. Alfredstelznerite sits at Mohs 2, 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; silky in aggregates.
4
Match the color range
Compare against the expected color range: colorless.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: prismatic crystals.

Often confused with

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

Often found alongside alfredstelznerite

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

All properties

Chemical formula: Ca₄B₁₆O₁₆(OH)₂₄·19H₂O
Mohs hardness: 2
Density: 1.77 g/cm³
Colors: Colorless
Streak: White
Luster: Vitreous; silky in aggregates
Transparency: Transparent, translucent on dehydration
Crystal system: Orthorhombic
Crystal habit: Prismatic crystals
Cleavage: Perfect on {010}
Rarity: Rare
Uses: Collector
Host rock: A secondary mineral in a cavity in fractured mudstone in a playa-hosted borate deposit

Where rockhounds find alfredstelznerite

Classic worldwide localities

Santa Rosa Mine, Sijes, Salta Province, Argentina

Field-hunting tip

Where it forms: A secondary mineral in a cavity in fractured mudstone in a playa-hosted borate deposit. If you start seeing colemanite, hydroboracite, ulexite in float, you are in the right ground. Typical habit: prismatic crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify alfredstelznerite?+

Mohs hardness is 2. Luster: vitreous; silky in aggregates. The streak is white. Common colors include colorless.

Where is alfredstelznerite found?+

Notable localities include Santa Rosa Mine, Sijes, Salta Province, Argentina.

What rocks look like alfredstelznerite?+

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

What minerals are found with alfredstelznerite?+

Alfredstelznerite commonly co-occurs with Colemanite, Hydroboracite, Ulexite, Inyoite, Gypsum, Anhydrite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does alfredstelznerite form in?+

Where it forms: A secondary mineral in a cavity in fractured mudstone in a playa-hosted borate deposit. Working float back to the host body is the standard way to chase a fresh occurrence.

What is alfredstelznerite used for?+

Alfredstelznerite is used in collector.

Find alfredstelznerite on the map

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