Hydrodelhayelite is an extremely rare phyllosilicate mineral typically found in alkaline igneous rocks. It is most easily identified by its characteristic pearly luster and platy habit, though it is usually only found as microscopic inclusions or small aggregates within host rocks.
Is this hydrodelhayelite?
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 hydrodelhayelite with a known reference. Hydrodelhayelite sits at Mohs ~4, 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.
- 4Match the color rangeCompare against the expected color range: white, pearl gray.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: platy or micaceous aggregates.
Often confused with
Hydrodelhayelite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside hydrodelhayelite
Minerals reported to co-occur with hydrodelhayelite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KCa₂(Si₇Al)O₁₇(OH)₂·6H₂O
- Mohs hardness
- ~4
- Density
- 2.168 g/cm³
- Colors
- WhitePearl gray
- Streak
- White
- Luster
- Vitreous
- Transparency
- Semitransparent
- Crystal system
- Orthorhombic
- Crystal habit
- Platy or micaceous aggregates
- Cleavage
- {010}, very perfect; {100} and {001}, imperfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary alteration product of delhayelite from ijolite-urtite pegmatites in a differentiated alkalic massif
Where rockhounds find hydrodelhayelite
Classic worldwide localities
- Mts. Rasvumchorr and Yukspor, in the Khibiny massif, Kola Peninsula, Russia
Field-hunting tip
Where it forms: A secondary alteration product of delhayelite from ijolite-urtite pegmatites in a differentiated alkalic massif. If you start seeing delhayelite, lamprophyllite, eudialyte in float, you are in the right ground. Typical habit: platy or micaceous aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify hydrodelhayelite?+
Where is hydrodelhayelite found?+
What rocks look like hydrodelhayelite?+
What minerals are found with hydrodelhayelite?+
What kind of rock does hydrodelhayelite form in?+
What is hydrodelhayelite used for?+
Find hydrodelhayelite on the map
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