Holtedahlite is a rare magnesium phosphate mineral typically found as transparent to translucent tabular crystals or granular aggregates. It is primarily known from metasomatic zones within serpentinized ultramafic rocks and is a highly sought-after specimen for advanced mineral collectors.

Hardness

4.5-5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Holtedahlite

Hardness: 4.5-5
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this holtedahlite?

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 holtedahlite with a known reference. Holtedahlite sits at Mohs 4.5-5, 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, granular.

Often confused with

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

mineral

Ludwigite

Mohs 5-5.5

How to tell apart: Streak differs, so Holtedahlite leaves white, Ludwigite leaves black to greenish black; luster reads vitreous on Holtedahlite and submetallic on Ludwigite.

Often found alongside holtedahlite

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

All properties

Chemical formula: Mg₁₂(PO₃OH,CO₃)(PO₄)₅(OH,O)₆
Mohs hardness: 4.5-5
Density: 2.94 g/cm³
Colors: Colorless
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Trigonal
Crystal habit: Tabular crystals, massive, granular
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: In a serpentine–magnesite deposit (Tingelstadtjern quarry, Norway); a common accessory mineral, of likely pneumatolytic origin, in an igneous magnetite–apatite deposit (Gole Gohar, Iran)

Where rockhounds find holtedahlite

Classic worldwide localities

Tingelstadtjern quarry, Modum, Norway
Into the millions of tons at the Gole Gohar iron deposit, Bafq district, Iran

Field-hunting tip

Where it forms: In a serpentine–magnesite deposit (Tingelstadtjern quarry, Norway); a common accessory mineral, of likely pneumatolytic origin, in an igneous magnetite–apatite deposit (Gole Gohar, Iran). If you start seeing althausite, szaibelyite, apatite 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 holtedahlite?+

Mohs hardness is 4.5-5. Luster: vitreous. The streak is white. Common colors include colorless.

Where is holtedahlite found?+

Notable localities include Tingelstadtjern quarry, Modum, Norway; Into the millions of tons at the Gole Gohar iron deposit, Bafq district, Iran.

What rocks look like holtedahlite?+

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

What minerals are found with holtedahlite?+

Holtedahlite commonly co-occurs with Althausite, Szaibelyite, Apatite, Talc, Magnetite, Magnesite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does holtedahlite form in?+

Where it forms: In a serpentine–magnesite deposit (Tingelstadtjern quarry, Norway); a common accessory mineral, of likely pneumatolytic origin, in an igneous magnetite–apatite deposit (Gole Gohar, Iran). Working float back to the host body is the standard way to chase a fresh occurrence.

What is holtedahlite used for?+

Holtedahlite is used in collector.

Find holtedahlite on the map

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