Amethyst (variety of Quartz)
Current inventory:  0 gems
 

  
Amethyst is named from the Greek word amethystos, meaning not drunken because the Greeks believed that drinking from an Amethyst cup would prevent intoxication.

Discovered in prehistory;   IMA status:  Not Valid (a variety of Quartz)

Chemistry

Chemical Formula:

SiO₂

Silicon Dioxide

Molecular Weight:

60.08 gm

Composition:

Silicon

46.74 %

Si

100.00 %

SiO₂

Oxygen

53.26 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Oxides

Strunz 8th Ed. ID:

4/D.01-10

Nickel-Strunz 10th Ed. ID:

4.DA.05

4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
D : Metal: Oxygen = 1:2 and similar
A : With small cations: Silica family

Related to:

Quartz is a polymorph of Coesite, Cristobalite, Stishovite and Tridymite.

Members of Group:

n/a

Varieties:

Hair Amethyst

Synonyms:

Amethystine Agate, Amethystine quartz, Bishops Stone, Lavendine, Spirit Quartz

Crystal Data

Crystallography:

Trigonal - Trapezohedral

Crystal Habit:

As enantimorphic prismatic crystals; may be morphologically complex, with over 500 forms noted, to 6 meters and 36 tons;
Crystalline - Coarse - Occurs as well-formed coarse sized crystals;
Crystalline - Fine - Occurs as well-formed fine sized crystals;
Druse - Crystal growth in a cavity which results in numerous crystal tipped surfaces.

Twinning:

Very common, penetration twins on the Dauphiné law, about [0001], and the Brazil law, with [1120] as contact plane; contact twins on the Japan law, with [1122] as contact plane, may be repeated; and several other laws.

Physical Properties

Cleavage:

None or [0110] Indistinct

Fracture:

Conchoidal

Tenacity:

Brittle

Moh's Hardness:

7.0

Density:

2.60 - 2.65 (g/cm³)

Luminescence:

May be Triboluminescent; varies widely due to traces of impurities.

Radioactivity:

Not Radioactive

Other:

Piezoelectric and Pyroelectric and may be Triboluminescent

Optical Properties

Color:

Pale Lilac, Violet, Purple

Transparency:

Transparent

Luster:

Vitreous (Glassy)

Refractive Index:

1.544 - 1.553  Uniaxial ( + )

Birefringence:

0.0090

Dispersion:

0.013

Pleochroism:

Weak

Occurances

Geological Setting:

In hydrothermal veins, epithermal to alpine; characteristic of granites and granite pegmatites; in sandstones and quartzites, less abundant in other rock types; in hydrothermal metal deposits. Common in carbonate rocks; a residual mineral in soils and sediments.

Common Associations:

Calcite, Chlorite, Epidote, Feldspars, Fluorite, Micas, Zeolites, many other species

Common Impurities:

Fe

Type Locality:

None (prehistoric)

Year Discovered:

Prehistoric

View mineral photos:

Amethyst Mineral Photos and Locations

More Information

Mindat.org  (Amethyst)
Mindat.org  (Quartz)
Webmineral.com  (Quartz)

Amethyst is the purple variety of Quartz and has been associated with royalty throughout history. Quartz is one of the most common minerals on Earth. Other varieties of Quartz include Ametrine and Citrine. Amethyst comes in a variety of colors, from pale violet to deep purple with red flashes. The color is due to trace amounts of iron impurities added to the basic silicon dioxide formula.

Amethyst is available from sources worldwide with notable occurances in Brazil; Mexico; Namibia; Nigeria; Uraguay; Arizona and North Carolina, USA; USSR; and Zambia.
 

  
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