Raymond Vilbikaitis, age 14, of St. Catharines,

What makes some minerals shine in the dark?

The prospector or the up‑to‑date rock hound may take a quartz lamp along on a field trip. Its ultraviolet beams will cause certain minerals to glow in the dark with tell‑tale colors, Pale, creamy opal glows with a vivid green light. A lump of drab calcite may glow with a sunset red. By using an ultraviolet light, a prospector can separate scheele, which is a valuable ore of tungsten, from minerals which look just like it under ordinary light.

Minerals which glow with fairy colors in the dark are said to be fluorescent or phosphorescent. Short wave ultraviolet rays are invisible to our eyes and give off no light. But when striking these minerals in the dark, they cause them to glow with identifying colors. Some rocks also give off these eerie colors when exposed to X‑rays or ordinary heat. Minerals which stop glowing when the source of radiation is shut off are said to be fluorescent. Those which keep on glowing for a while are said to be phosphorescent,

Ultraviolet, X‑rays and ordinary heat are, of course, various forms of energy. And it takes energy to start the fluorescent or phosphorescent process going in the minerals. The energy is thought to jolt a number of. electrons out of place in the solid mineral, After the jolt, each electron returns to its original position and in doing so gives up this captured energy in the form of light. .

You might be able to cause the same thing to happen on a small scale with a lump of sugar. Make sure your eyes are quite used to the dark room, then break the sugar crystal apart with all your might. The sudden energy may jolt a few electrons and, if the experiment is lucky, you will see a glowing spark as the tiny particles drop back into position.

The fascinating study of these glowing minerals is fairly new and often confusing. Sometimes a non‑fluorescent mineral will glow under ultraviolet because of small impurities of some fluorescent mineral. Of two specimens of the same rock taken from different areas, one may glow and the other may not. As studies go on, we get more information and learn to identify more and more minerals from the color of the fluorescence or phosphorescence under ultraviolet, X‑rays, heat or even sunlight.

All the uranium minerals are fluorescent and so are most of the phosphate minerals. Celestite, a phosphate crystal of palest blue glows undor ultraviolet with bright yellowish green. The sulphate mineral barite gives off a bright orange fluorescence after roasting and continues to glow with phosphorescent light for some time. Various colored crystals of fluorite also glow in the dark after heating. And a diamond will sometimes glow with phosphorescent light after being exposed to ordinary sunlight,