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: Amethyst

Amethyst & Rose De France Gemstones

Rough & Faceted Amethyst Crystals

Source: Brazil, Uruguay, Zambia

Birthstone: February (Alternate: Onyx)

The name "amethyst" comes from the Greek word meaning "against drunkenness." This was perhaps due to a belief that amethyst would ward off the effects of alcohol, but most likely the Greeks were referring to the wine-like color of some varieties of the stone. Amethyst is the purple variety of the mineral quartz and is a popular gemstone. Amethyst can occur as elongated prismatic crystals which have a six sided pyramid at either end. They can also form as druze which are crystalline encrustations, typically within geodes, that only show the pointed terminations of each crystal.

As stated above, amethyst belongs to the quartz family of minerals, and is classified as a tectosilicate. Quartz is one of the most commonly found minerals within the earth's crust. The chemical silica dioxide is the principle component in quartz as well as most other igneous rocks. Amethyst is formed from silica-rich liquids deposited in gas cavities or geodes within lava.

Rose Amethyst Geode Rough

Rose Amethyst Geode

   Fantasy Cut Amethyst

Fantasy Cut Amethyst

The amethyst variety of quartz derives its purple color from trace amounts of iron that have been oxidized from exposure to naturally occurring ionizing-radiation that is a byproduct of the decay of potassium 40. The color purple has long been associated with royalty, making amethyst jewelry a popular choice among royal families.

Amethyst Crystal Structure

Amethyst is typically associated with igneous rock, grown in pegmatites and geodes that formed during the mountain building process. Being a variety of quartz, amethyst crystalizes in the rhombohedral crystal system (trigonal-trapezohedral), with an "enantiomorphic" and prismatic crystal habit, forming left-right 'Brazil-law' twins (above, center), v-shaped 'Japan-law' twins (above, right), or 'DauphinŽ-law' twins of 6-sided prisms; each ending in 6-sided pyramids. Like all quartz, amethyst is Piezoelectric.

Amethyst (Quartz) Crystallography, Chemistry, Physical Properties

Crystal System trigonal, hexagonal (trigonal-trapezohedral)
Crystal Habit enantiomorphic, prismatic
Specific gravity (SG) 2.65
Mohs Hardness Scale 7.0 to 7.5
Toughness good
Fracture conchoidal
Cleavage weak in three directions
Streak white
Chemical Composition SiO2 (quartz: silicon dioxide)

Amethyst (Quartz) Optical Properties

Optical Properties double refractive
Refractive Index 1.544 to 1.553
Birefringence +0.009 (B-G interval)
Pleochroism/Dichroism weak dichroism
Surface Luster vitreous (glassy)
Diaphaneity transparent, translucent, sub-translucent
Gem Color bluish-purple, pink, purple

Natural purple amethyst will turn to citrine when heated in a kiln for a certain period of time and much of the yellow, gold, or orange citrine on the market today is heat-treated amethyst.

Rose De France (Rose Amethyst)

Rose colored amethyst, known as "Rose De France" is a very light pink to pinkish-mauve colored amethyst gemstone that is typically from Brazil. The color of Rose De France is similar to the pale pink variety of beryl known as morganite which is also from Brazil.

Amethyst heat treatment is used if the natural color of the stone is too dark. The heat treatment is used to lighten the color to a rich purple or change the color entirely. Amethyst can also be irradiated to improve color.

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Bibliography and Reference on Amethyst

1. Judith Crowe, The Jeweler's Directory of Gemstones . DK Publishing.

2. A.C. Akhavan, Twinning in Quartz Crystals www.quartzpage.de

3. GIA, Characteristics of Citrine, Amethyst & Smoky Quartz www.gia.edu

4. Renee Newman, Gemstone Buying Guide . International Jewelry Publications; 2nd edition

5. Antoinette L . Matlins, Antonio C. Bonanno, Gem Identification Made Easy . Gemstone Press

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