Amethyst with standing surface and polished edge in jellyfish. B (commercial grade)

Amethyst, a violet quartz mineral (SiO2), is the most coveted variant within the quartz group. The name comes from the Greek 'amethystos'. Known to the Egyptians, Etruscans and Romans, amethyst was described by Pliny the Elder. In ancient China they made small gems from it. In the Middle Ages, amethyst was very popular in Europe and was known as 'bishop's stone', popular with church leaders and attributed with magical properties. It symbolized love, temperance and protection against sorcery and witchcraft. Jacob van Maerlant stated that the stone prevents drunkenness, which is related to the Greek meaning 'against intoxication'; it was believed that wine from an amethyst cup was not intoxicating. Amethyst is formed in metamorphites, hydrothermal vents and alluvial deposits, growing on an underlayer. The prisms are often weak, allowing the crystal spiers to dominate; here the color is most intensive. Heating between 470 and 750 degrees produces light yellow, reddish brown, green or colorless varieties. Some amethysts fade in daylight, but their color can be restored with radium irradiation. The color is due to iron in combination with ionizing radiation. Amethyst is less attractive under artificial light. Brazil, known for its amethyst deposits since the Middle Ages, mines them mainly in Bahia, Minas Gerais and Mato Grosso. Recently 'ametrine' has been mined in Bolivia, a combination of amethyst and citrine with alternating violet and yellow colours. However, the transition between the colors is sharply defined.