'Purple Rain' Weardale fluorite twins

Locality: Purple Rain Pocket, Lady Annabella Mine, Weardale, County Durham, England

Approx size: 1/2–1"

Approx weight: 8–12g

❗Sunlight will fade the color in fluorite. Keep sun exposure brief; do not display in a sun-exposed location (even if it looks cool!)

Weardale is among the most renowned sources for fluorite among collectors, producing gemmy cubic crystals with Jolly-Rancher colors and strong UV reactivity. These twinned cubic crystals come via UK Mining Ventures, who currently own and operate the famed Lady Anabella, Rogerly, and Diana Maria mines in Weardale.

The Purple Rain Pocket is part of the Fairy Hole Vein in the Lady Annabella mine. The find earned its name from the steady rains that accompanied the pocket's extraction, paired with the material's intense purple daylight fluorescence. Daylight fluorescence means the fluorite reacts to the UV in sunlight, taking on an other-worldly indigo glow.

Purple Rain specimens typically appear a murky dark purple-gray color under incandescent light (indoor lighting). Under closer inspection the variety displays good color zoning, with alternating thin bands of violet, amethyst, magenta, mauve, and light green visible at the edges. The alternating zones of green and purple muddle to give the material its distinctive inky grape-soda appearance.

'Twinning' is very common in Weardale fluorite and means that two or more fluorite crystals have intergrown, and actually share the same crystal lattice. They appear as though one cube is embedded inside the other, so that its corners poke out of the faces of the other cube. The crystals are marked by geometric striations across many faces, easiest to view in reflected light. These striations radiate out from where the edge of the intersecting crystal breaks the surface of the face. The example highlighted in the second image is from Option D.

You may see small pits spotting the faces of your specimen; under magnification they are inverted four-sided pyramids—basically, half of an octahedron. This is caused by natural etching just like trigons in diamonds, and the etch pits can cover the face enough to cause a sheen effect. Etching also causes the diagonal cross-hatched pattern on the face of some crystals, as the etching effectively highlights the mineral's natural cleavage planes.

UV Reactivity: Weardale fluorites have high rare earth element content, contributing to their strong UV reaction. These Purple Rain specimens react with a strong light blue glow under several UV wavelengths, and they are very bright when exposed to a powerful 365nm UV light. I detected weak to moderate phosphorescence that lingers several seconds (5+ secs) after exposure to 365nm.

☀ The daylight fluorescence effect was photographed on a cloudy day; I find the glow appears the most intense in indirect or diffused sun—for example, enjoy your fluorite outdoors on an overcast day, or near a window indoors.