This large geode structure of amethyst is on display in the Smithsonian Museum of Natural History. Amethyst is a variety of quartz with the characteristic composition SiO2, but distinctive and popular for its dramatic purple color.

This geode is about 40x35 cm and is from Rio Grande do Sul, Brazil. It is described as amethyst formed with calcite.

This interesting formation of amethyst quartz crystals is about 24x40 cm and is from Sweden, Maine.

This is a closer view of one of the crystal clusters of the sample at left.

The large single crystal of amethyst at right is about 4x4 cm and is from North Carolina. The gem below it is 1362 carats and is from Jacobea mine, Bahia, Brazil. The sample extreme right is about 17x15 cm and is from Diamond Willow mine, Pearl, Ontario,Canada.

This sample is about 10x7 cm and is from Vera Cruz, Mexico.

This huge display of amethyst crystals is about 60x60 cm and is from Guerrero, Mexico.

This sample of amethyst is about 7x7 cm. It is from Rio Grande do Sul, Brazil

This example of amethyst crystals is about 35x40 cm. It is presumed that amethyst crystals formed first in an underground cavity from water containing dissolved silica. Later, another solution entered the cavity and formed the calcite crystals on top.

This large specimen of amethyst crystals is probably 60 cm across. It is from Serra do Mar, Rio Grande do Sul, Brazil. It was once part of a 32,000 kg (70,000 lb) geode.

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