Gyrolite is a fascinating silicate mineral that typically forms distinct, spherical radiating clusters or globular masses within basalt cavities. It is easily recognized by its characteristic pearly luster and white to pale yellow color. Collectors often prize it for its association with beautiful zeolite minerals like apophyllite and prehnite.
Is this gyrolite?
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 gyrolite with a known reference. Gyrolite sits at Mohs 3-4, 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, brown, colorless, yellow, light green.
- 5Look at form & habitCrystal system: triclinic. Typical habit: compact, lamellar, platy.
Often confused with
Gyrolite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside gyrolite
Minerals reported to co-occur with gyrolite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaCa₁₆(Si₂₃Al)O₆₀(OH)₈·14H₂O
- Mohs hardness
- 3-4
- Density
- 2.388-2.390 g/cm³
- Streak
- White
- Luster
- Vitreous to pearly
- Transparency
- Transparent to translucent, opaque
- Crystal system
- Triclinic
- Crystal habit
- Compact, lamellar, platy
- Cleavage
- Perfect basal; poor prismatic
- Fluorescence
- White under SW and LW UV
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- As replacements of wall rocks and in vugs, amygdules, and veinlets in basalts; in hydrothermally altered rhyolites and sediments; in some ore deposits
Where rockhounds find gyrolite
1 mapped spotsClassic worldwide localities
- Fort Point, San Francisco Co., and in the New Almaden mine, Santa Clara Co., California, USA
- Yellowstone National Park, Wyoming, USA
- Goose Creek quarry, Leesburg, Loudoun Co., Virginia, USA
- Portree, Isle of Skye and 'S Airde Beinn, Isle of Mull, Scotland
- Ballhenry, Co. Antrim, Ireland
- Ortano, Elba, and at Monte Biaena, Pannone, Trentino-Alto Adige, Italy
Field-hunting tip
Where it forms: As replacements of wall rocks and in vugs, amygdules, and veinlets in basalts; in hydrothermally altered rhyolites and sediments; in some ore deposits. If you start seeing apophyllite, stilbite, laumontite in float, you are in the right ground. Typical habit: compact, lamellar, platy. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in California. Start trip planning there.
Common questions
How do you identify gyrolite?+
Where is gyrolite found?+
Can I find gyrolite in the United States?+
What rocks look like gyrolite?+
What minerals are found with gyrolite?+
What kind of rock does gyrolite form in?+
What is gyrolite used for?+
Find gyrolite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
