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Photograph of a large cushion-cut amethyst (G9575) from the National Gem Collection
Photo by Chip Clark
QuartzAll quartz have the same arrangement of silicon and oxygen atoms. Because they grew under different conditions, they exhibit an incredible variety of shapes and colors. Impurities cause the distinctively colored gem varieties: rose quartz (pink); citrine (yellow or gold); amethyst (purple); and smoky quartz (black or brown).
Hover over color tiles above to learn what this object tells us about the history of the Earth
About this object
Quartz, one of the most abundant minerals in the Earth’s crust, is composed of silicon and oxygen and in its pure state is colorless. When iron replaces some of the silicon atoms, the color is purple. Purple quartz is called amethyst and is the most prized gem variety of quartz. Amethyst is found in a variety of geologic settings, but most commmonly as crystals lining cavities in volcanic rock. The major sources for amethyst are Brazil and Uruguay. This modified rectangular cut amethyst from Brazil is 109.66 carats.
denotes specimens currently on exhibit
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