Raw fluorescent Yooperlite, stone that glows under UV light - FIREFLY

Yooperlite is the name given to a syenite, an igneous rock rich in feldspars, which contains grains of fluorescent sodalite. It was noticed on the shores of Lake Superior, in Michigan's Upper Peninsula, USA, where the inhabitants are nicknamed "Yoopers." In daylight, it looks like a simple grey pebble; under an ultraviolet lamp, the sodalite glows in orange-yellow. It is therefore not a mineral species in its own right, but a rock whose interest lies in its fluorescence. We do not guarantee the exact collection location of the stones offered here.

No, the UV lamp is not included: the one that appears in some photos is only used to show the effect. To observe fluorescence, you need a long-wave ultraviolet lamp, ideally 365 nm. These small flashlights are easy to find. The more common 395 nm models emit more visible violet light and often give a less distinct effect. It is best to use them in a dark room. If you are giving the stone as a gift, consider providing a lamp at the same time: the discovery will be immediate and much more spectacular.

A fluorescent stone absorbs ultraviolet radiation and re-emits visible light only while it is being illuminated: as soon as you turn off the lamp, it returns to grey. A phosphorescent material, like some paints or self-adhesive stars, conversely continues to glow for a few seconds or minutes after the source is turned off. Yooperlite is fluorescent: it does not "charge" and does not glow on its own in the dark. This is what makes the experience so interesting, as you can see very clearly that the emitted light depends directly on the UV illumination received.

Batches are sold by weight: 200g, 400g, or 500g. The number of stones is therefore not fixed and depends on the size of the stones in the batch, which varies from one harvest to another. A batch may thus contain a few large stones and several smaller ones. The 1-piece format corresponds to one stone of about 3 to 4 cm. Since each stone is natural and raw, its appearance, shape, and fluorescence intensity differ: this is precisely what makes it interesting to compare several specimens under the lamp.

The photos show yooperlite as aquarium decoration, where its orange sparks stand out beautifully under UV lighting. Before any immersion, we advise you to rinse the stones thoroughly with clean water, without soap or chemicals, to remove dust and residue. We do not have supplier information on the possible effect of these stones on water chemistry: for a populated aquarium, especially with sensitive species, monitor water parameters after adding them and consult your usual specialist. In an empty aquarium or a decorative terrarium, their use is fine.

Small hobby UV lamps can be used without difficulty by following a few simple rules: never look directly at the source, do not point the beam at anyone's eyes or at an animal, and avoid prolonged skin exposure. Ultraviolet light is invisible, so the eye does not reflexively protect itself as it would against bright light. Children must use the lamp under adult supervision. UV-filtering glasses can be useful for prolonged observations. The stone itself does not emit any radiation: it simply converts the UV it receives into visible light.

Yooperlite is a robust rock for daily use. A rinse with clear water and air drying are enough to clean it; a soft brush can be used to remove dust lodged in the crevices. Avoid household cleaning products, acids, and detergents. Store the stones in a bowl, box, or display case, away from impacts, to prevent them from chipping. Fluorescence does not fade over time: you can repeat the experiment as many times as you like, the effect remains the same.