Yooperlite is the marketing name for clasts of syenite-rich rocks containing fluorescent sodalite found on the shores of Lake Superior. Under normal daylight, these stones appear as unassuming gray or brownish rocks, but they exhibit a striking bright orange-yellow glow when exposed to ultraviolet light. Collectors typically hunt for these at night along beaches using handheld UV flashlights.
Is this yooperlite?
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 yooperlite with a known reference. Yooperlite sits at Mohs 6, softer than the next harder reference, harder than the previous one.
- 2Read the textureLook at a fresh break with a hand lens. Grain size: Coarse-grained.
- 3Pick out the mineralsComposition: Syenite containing fluorescent sodalite (sodalite-syenite). Identify the two or three most abundant grains.
- 4Read the lusterHold the specimen under a strong light. Luster: vitreous to greasy.
- 5Match the color rangeCompare against the expected color range: gray, gray-brown.
Often confused with
Yooperlite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside yooperlite
Minerals reported to co-occur with yooperlite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 6
- Density
- 2.3-2.4 g/cm³
- Colors
- Luster
- Vitreous to greasy
- Transparency
- Translucent
- Fluorescence
- Bright orange-yellow under SW and LW UV
- Rarity
- Common
- Uses
- Collector, Lapidary
- Host rock
- Syenite
- Grain size
- Coarse-grained
- Composition
- Syenite containing fluorescent sodalite (sodalite-syenite)
Where rockhounds find yooperlite
22 mapped spotsClassic worldwide localities
- Lake Superior shores, Michigan, USA
- Ontario, Canada
U.S. states with yooperlite
Each link opens a state-specific list of mapped rockhounding spots that produce yooperlite.
Field-hunting tip
Where it forms: Syenite. If you start seeing syenite, microcline, nepheline in float, you are in the right ground. In the U.S., the densest reported localities are in Michigan. Start trip planning there.
More yooperlite photos
Common questions
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Can I find yooperlite in the United States?+
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Find yooperlite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
