Kalsilite is a rare potassium-dominant member of the nepheline group, typically occurring in silica-undersaturated volcanic rocks. It is visually difficult to distinguish from nepheline without X-ray diffraction or chemical analysis. Collectors typically seek it in association with rare volcanic suites in the Eifel region or its type locality in Uganda.
Is this kalsilite?
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 kalsilite with a known reference. Kalsilite sits at Mohs 6, 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 greasy.
- 4Match the color rangeCompare against the expected color range: colorless, gray, gray white, white.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: equant to prismatic crystals, often as microscopic grains or interstitial fillings.
Often confused with
Kalsilite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside kalsilite
Minerals reported to co-occur with kalsilite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KAlSiO₄
- Mohs hardness
- 6
- Density
- 2.59-2.62 g/cm³
- Streak
- White
- Luster
- Vitreous to greasy
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Equant to prismatic crystals, often as microscopic grains or interstitial fillings
- Cleavage
- Poor on {1010}, {0001}
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- In the groundmass of some potassium-rich and silica-deficient lavas and tuffs; rare in syenites; may be formed by the breakdown of silica-rich leucite in alkalic ultramafic rocks; from a granulite-facies emery deposit
Where rockhounds find kalsilite
Classic worldwide localities
- Mafuru and Katunga craters, Uganda
- Congo (Zaire), in the Baruta crater, Nyiragongo area, Kivu Province
- Monte Somma and Vesuvius, Campania, Italy
- Ariccia, near Rome, Lazio, Italy
- San Venanzo and Pian di Celle volcanos, Umbria, Italy
- Batbjerg alkalic ultramafic intrusion, Kangerdlugssuaq Glacier, Greenland
Field-hunting tip
Where it forms: In the groundmass of some potassium-rich and silica-deficient lavas and tuffs; rare in syenites; may be formed by the breakdown of silica-rich leucite in alkalic ultramafic rocks; from a granulite-facies emery deposit. If you start seeing olivine, melilite, clinopyroxene in float, you are in the right ground. Typical habit: equant to prismatic crystals, often as microscopic grains or interstitial fillings. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify kalsilite?+
Where is kalsilite found?+
What rocks look like kalsilite?+
What minerals are found with kalsilite?+
What kind of rock does kalsilite form in?+
What is kalsilite used for?+
Find kalsilite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
