Calcite is transparent to opaque and may occasionally show phosphorescence or fluorescence. A small amount of manganese is enough to make it glow bright red under some wave lengths of ultraviolet light.
Amethyst is a violet variety of quartz often used in jewelry. Amethyst occurs in primary hues from a light pinkish violet to a deep purple. Amethyst may exhibit one or both secondary hues, red and blue. The best varieties of amethyst can be found in Siberia, Sri Lanka, Brazil and the far East.
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a non-profit organization dedicated to the knowledge of earth sciences
