Phillipsite-K is a zeolite mineral known for its complex cruciform penetration twinning, often forming radiating 'x-shaped' crystal clusters. It is typically found in the vesicles of basaltic rocks and other volcanic environments where it forms through the alteration of glassy volcanic material.
Is this phillipsite-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 phillipsite-k with a known reference. Phillipsite-K sits at Mohs 4-5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Phillipsite-K leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Phillipsite-K typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, yellow, red, brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: cruciform penetration twins, radiating clusters, prismatic.
Often confused with
Phillipsite-K vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside phillipsite-k
Minerals reported to co-occur with phillipsite-k. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (K,Na,Ca)₃₋₄(Si,Al)₁₆O₃₂·12H₂O
- Mohs hardness
- 4-5
- Density
- 2.2 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Cruciform Penetration Twins, Radiating Clusters, Prismatic
- Cleavage
- Distinct On {010} and {110}
- Rarity
- Common
- Uses
- Collector
- Host rock
- Basaltic Volcanic Rocks, Cavities in Amygdaloidal Basalts
- Typical price
- $10-50 per specimen
Where rockhounds find phillipsite-k
Classic worldwide localities
- Vesuvius, Italy
- Giessen, Germany
- Table Mountain, Colorado, USA
- Giant's Causeway, Northern Ireland
- Skye, Scotland
Field-hunting tip
Look in basaltic volcanic rocks, cavities in amygdaloidal basalts country — that is the host setting where phillipsite-k typically forms. If you start seeing calcite, analcime, natrolite in float, you are in the right ground. Field specimens usually show a cruciform penetration twins, radiating clusters, prismatic habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify phillipsite-k?+
Where is phillipsite-k found?+
How much is phillipsite-k worth?+
What rocks look like phillipsite-k?+
What minerals are found with phillipsite-k?+
What kind of rock does phillipsite-k form in?+
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Find phillipsite-k on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
