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. Hydroxyapophyllite-(K) leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Hydroxyapophyllite-(K) typically shows a vitreous to pearly luster.
- 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.
How to tell apart: Luster reads vitreous to pearly on Hydroxyapophyllite-(K) and vitreous on Stilbite.
How to tell apart: Quartz is the harder of the two (Mohs 7 vs. 4.5-5); luster reads vitreous to pearly on Hydroxyapophyllite-(K) and vitreous on Quartz.
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
- Typical price
- $10-150 for specimens depending on size and crystal clarity
Where rockhounds find hydroxyapophyllite-(k)
Classic worldwide localities
- Pune, India
- Pooona, India
- Kongsberg, Norway
- Andreasberg, Germany
- Mont Saint-Hilaire, Canada
Field-hunting tip
Look in basaltic vugs and cavities in amygdaloidal basalt country — that is the host setting where hydroxyapophyllite-(k) typically forms. If you start seeing stilbite, heulandite, laumontite in float, you are in the right ground. Field specimens usually show a prismatic or tabular crystals often with pyramidal terminations, sometimes blocky habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify hydroxyapophyllite-(k)?+
Where is hydroxyapophyllite-(k) found?+
How much is hydroxyapophyllite-(k) worth?+
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
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