Hiortdahlite is a rare sorosilicate mineral typically found in nepheline syenite pegmatites. Collectors look for its characteristic pale yellow to colorless tabular crystals, which are often associated with other rare alkaline accessory minerals.
Is this hiortdahlite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch hiortdahlite with a known reference. Hiortdahlite sits at Mohs 5.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous on crystal faces, greasy on fractures.
- 4Match the color rangeCompare against the expected color range: brown, colorless, yellow brown, honey yellow, light yellow.
- 5Look at form & habitCrystal system: triclinic. Typical habit: tabular.
Often confused with
Hiortdahlite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside hiortdahlite
Minerals reported to co-occur with hiortdahlite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₂Ca₄(Ca₀.₅Zr₀.₅)Zr(Si₂O₇)₂OF₃
- Mohs hardness
- 5.5
- Density
- 3.25-3.31 g/cm³
- Streak
- White
- Luster
- Vitreous on crystal faces, greasy on fractures
- Transparency
- Semitransparent
- Crystal system
- Triclinic
- Crystal habit
- Tabular
- Cleavage
- Distinct on {110} and {110}, the two intersecting at nearly 90°
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare mineral in alkalic rocks, their pegmatites, and metamorphosed equivalents; in miarolitic cavities in sanidinites
Where rockhounds find hiortdahlite
Classic worldwide localities
- Mittel Arø, Lille Arø, and Stokkø Islands, in the Langesundsfjord, Norway
- Monte Somma and Vesuvius, Campania, Italy
- Mayen, Eifel district, Germany
- Kangerdlugssuaq Fjord, Greenland
- Korgeredaba massif, Sangilen, Tuva, Russia
- Los Islands, Guinea
Field-hunting tip
Where it forms: A rare mineral in alkalic rocks, their pegmatites, and metamorphosed equivalents; in miarolitic cavities in sanidinites. If you start seeing feldspar, biotite, meliphanite in float, you are in the right ground. Typical habit: tabular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify hiortdahlite?+
Where is hiortdahlite found?+
What rocks look like hiortdahlite?+
What minerals are found with hiortdahlite?+
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What is hiortdahlite used for?+
Find hiortdahlite on the map
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