Ernstite is a rare phosphate mineral that forms through the oxidation of eosphorite in pegmatite environments. It typically occurs as prismatic crystals or radial sprays with a distinct yellowish to reddish-brown coloration, often found in association with other phosphate minerals.

Hardness

3-3.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Semitransparent

mineralrareChildrenite-Eosphorite Group family

Ernstite

Hardness: 3-3.5
Luster: Vitreous
Streak: White
Transparency: Semitransparent

Is this ernstite?

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 ernstite with a known reference. Ernstite sits at Mohs 3-3.5, 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: yellow brown.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: aggregates, radial.

Often confused with

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

mineral

Eosphorite

Mohs 5

How to tell apart: Eosphorite is the harder of the two (Mohs 5 vs. 3-3.5).

How to tell apart: Childrenite is the harder of the two (Mohs 5 vs. 3-3.5).

Compare →

Often found alongside ernstite

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

Eosphorite
mineral · Mohs 5

All properties

Chemical formula: (Mn²⁺,Fe³⁺)Al(PO₄)(OH,O)₂·H₂O
Mohs hardness: 3-3.5
Density: 3.07 g/cm³
Colors: Yellow brown
Streak: White
Luster: Vitreous
Transparency: Semitransparent
Crystal system: Monoclinic
Crystal habit: Aggregates, radial
Cleavage: On {100}, very good; on {010}, good
Rarity: Rare
Uses: Collector
Host rock: Formed by oxidation of eosphorite in a granite pegmatite (Farm Davib-East, Namibia)

Where rockhounds find ernstite

Classic worldwide localities

Found on the Farm Davib-East, near Karibib, southern Erongo Mountains, Namibia
St. John’s quarry, near Kapunda, Mount Lofty Ranges, South Australia

Field-hunting tip

Where it forms: Formed by oxidation of eosphorite in a granite pegmatite (Farm Davib-East, Namibia). If you start seeing eosphorite in float, you are in the right ground. Typical habit: aggregates, radial. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify ernstite?+

Mohs hardness is 3-3.5. Luster: vitreous. The streak is white. Common colors include yellow brown.

Where is ernstite found?+

Notable localities include Found on the Farm Davib-East, near Karibib, southern Erongo Mountains, Namibia; St. John’s quarry, near Kapunda, Mount Lofty Ranges, South Australia.

What rocks look like ernstite?+

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

What minerals are found with ernstite?+

Ernstite commonly co-occurs with Eosphorite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does ernstite form in?+

Where it forms: Formed by oxidation of eosphorite in a granite pegmatite (Farm Davib-East, Namibia). Working float back to the host body is the standard way to chase a fresh occurrence.

What is ernstite used for?+

Ernstite is used in collector.

Find ernstite on the map

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