Phillipsite-Ca is a common zeolite mineral recognized for its distinctive complex penetration twinning which often forms cross-shaped crystals. It is typically found lining amygdaloidal cavities in volcanic rocks or as authigenic crystals in marine deposits. Collectors should look for its classic cruciform habit, usually associated with other zeolites and calcite.
Is this phillipsite-ca?
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-ca with a known reference. Phillipsite-Ca 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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: white, reddish white, light yellow, pink.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic, pseudo tetragonal, twinning common.
Often confused with
Phillipsite-Ca vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside phillipsite-ca
Minerals reported to co-occur with phillipsite-ca. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₃(Si₁₀Al₆)O₃₂·12H₂O
- Mohs hardness
- 4-5
- Density
- 2.2 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic, pseudo tetragonal, twinning common
- Cleavage
- Distinct on {010}; indistinct on {001}
- Rarity
- Common
- Uses
- Collector, Scientific research
- Host rock
- Common zeolite in volcanic rocks, ore veins, diagenetically altered rhyolitic vitric tuffs, saline lake deposits, and ocean floor sediments
Where rockhounds find phillipsite-ca
Classic worldwide localities
- Lower Salt Lake Tuff, Puuloa Road near junction with Moanalua Road, Oahu, Hawaii (type locality)
Field-hunting tip
Where it forms: Common zeolite in volcanic rocks, ore veins, diagenetically altered rhyolitic vitric tuffs, saline lake deposits, and ocean floor sediments. If you start seeing calcite, analcime, natrolite in float, you are in the right ground. Typical habit: prismatic, pseudo tetragonal, twinning common. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify phillipsite-ca?+
Where is phillipsite-ca found?+
What rocks look like phillipsite-ca?+
What minerals are found with phillipsite-ca?+
What kind of rock does phillipsite-ca form in?+
What is phillipsite-ca used for?+
Find phillipsite-ca on the map
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