Ameghinite is a rare sodium borate mineral found almost exclusively in the evaporite deposits of Argentina. It typically forms colorless to white tabular crystals or massive aggregates within borate-rich lacustrine settings. Collectors prioritize specimens from the Tincalayu mine, where it is often associated with other borate species.

Hardness

2.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Ameghinite

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

Is this ameghinite?

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 ameghinite with a known reference. Ameghinite 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: monoclinic. Typical habit: tabular crystals, massive, granular.

Often confused with

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

Often found alongside ameghinite

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

All properties

Chemical formula: NaB₃O₃(OH)₄
Mohs hardness: 2.5
Density: 2.030 g/cm³
Colors: Colorless
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Tabular crystals, massive, granular
Cleavage: {100}, very good; {001} and {010}, poor
Fluorescence: Strong pale blue under SW and LW UV
Rarity: Rare
Uses: Collector
Host rock: Formed in massive borax in a borate-rich playa

Where rockhounds find ameghinite

Classic worldwide localities

Tincalayu borax deposit, Salar del Hombre Muerto, Salta Province, Argentina

Field-hunting tip

Where it forms: Formed in massive borax in a borate-rich playa. If you start seeing tincalconite, borax, ezcurrite in float, you are in the right ground. Typical habit: tabular crystals, massive, granular. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify ameghinite?+

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

Where is ameghinite found?+

Notable localities include Tincalayu borax deposit, Salar del Hombre Muerto, Salta Province, Argentina.

What rocks look like ameghinite?+

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

What minerals are found with ameghinite?+

Ameghinite commonly co-occurs with Tincalconite, Borax, Ezcurrite, Rivadavite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does ameghinite form in?+

Where it forms: Formed in massive borax in a borate-rich playa. Working float back to the host body is the standard way to chase a fresh occurrence.

What is ameghinite used for?+

Ameghinite is used in collector.

Find ameghinite on the map

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