Hydroxyapophyllite-(K) is highly sought after by collectors for its sharp, glassy, tetragonal crystal habits and aesthetic association with zeolites. It is frequently found lining vugs in volcanic basalt, where it displays a characteristic pearly luster on its perfect basal cleavage faces.
Is this hydroxyapophyllite-(k)?
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 hydroxyapophyllite-(k) with a known reference. Hydroxyapophyllite-(K) sits at Mohs 4.5-5, 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 to pearly.
- 4Match the color rangeCompare against the expected color range: white, colorless, green, yellow, pink.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: prismatic or tabular crystals often with pyramidal terminations, sometimes blocky.
Often confused with
Hydroxyapophyllite-(K) vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside hydroxyapophyllite-(k)
Minerals reported to co-occur with hydroxyapophyllite-(k). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KCa₄(Si₈O₂₀)(OH,F)·8H₂O
- Mohs hardness
- 4.5-5
- Density
- 2.3-2.4 g/cm³
- Streak
- White
- Luster
- Vitreous to pearly
- Transparency
- Transparent
- Crystal system
- Tetragonal
- Crystal habit
- Prismatic or tabular crystals often with pyramidal terminations, sometimes blocky
- Cleavage
- Perfect basal
- Rarity
- Common
- Uses
- Collector
- Host rock
- basaltic vugs and cavities in amygdaloidal basalt
Where rockhounds find hydroxyapophyllite-(k)
Classic worldwide localities
- Pune, India
- Pooona, India
- Kongsberg, Norway
- Andreasberg, Germany
- Mont Saint-Hilaire, Canada
Field-hunting tip
Where it forms: basaltic vugs and cavities in amygdaloidal basalt. If you start seeing stilbite, heulandite, laumontite in float, you are in the right ground. Typical habit: prismatic or tabular crystals often with pyramidal terminations, sometimes blocky. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify hydroxyapophyllite-(k)?+
Where is hydroxyapophyllite-(k) found?+
What rocks look like hydroxyapophyllite-(k)?+
What minerals are found with hydroxyapophyllite-(k)?+
What kind of rock does hydroxyapophyllite-(k) form in?+
What is hydroxyapophyllite-(k) used for?+
Find hydroxyapophyllite-(k) on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
