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Chemical Formula | SiO2 | ||||||||||||||||
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Composition | Silicon dioxide. Its purple coloring is caused by impurities of iron or manganese compounds. | ||||||||||||||||
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Color | Light to dark purple. Sometimes banded purple and white; sometimes mixed with colorless Rock Crystal; and sometimes mixed with brownish-yellow Citrine. | ||||||||||||||||
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Streak | White | ||||||||||||||||
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Hardness | 7 | ||||||||||||||||
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Crystal Forms and Aggregates |
(Hexagonal) Occurs as protruding clusters of
pyramids on a geode base. These "pyramids" can be
quite large. Also occurs as tall prismatic crystals, as short stubby crystals, in drusy aggregates, massive, in geodes, and as rounded waterworn stones. A very
interesting but strange habit is as crystalline crusts inside volcanic pipes. Crystals are usually striated horizontally, and occasionally have a scepter growth. |
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Transparency | Transparent to translucent | ||||||||||||||||
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Specific Gravity | 2.6 - 2.7 | ||||||||||||||||
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Luster | Vitreous | ||||||||||||||||
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Cleavage | Indiscernible | ||||||||||||||||
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Fracture | Conchoidal | ||||||||||||||||
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Tenacity | Brittle | ||||||||||||||||
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Other ID Marks | May fluoresce cream or white in shortwave ultraviolet light | ||||||||||||||||
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Varieties |  Amethyst Quartz - Mixture
of Amethyst and Milky Quartz (or clear Quartz). It is purple on
top and white or clear on the bottom. It may also be banded purple and white. Ametrine
- Mixture of Amethyst and Citrine. It is partially purple and partially
orange-yellow, with the color zones often sharply
divided. Canadian
Amethyst - Amethyst with an internal coating of
red Hematite. It is only found in Thunder Bay, Ontario. Lavender
Amethyst - Pale purple variety of Amethyst Veracruz
Amethyst - Tall, prismatic Amethyst crystals from Vera Cruz, Mexico. |
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In Group | Silicates ; Tectosilicates ; Silica group May also be classified as an oxide (Oxides ; Simple Oxides) |
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All About | Amethyst is a well known gem. It is variety of Quartz, which contains many other gemstones, such as Citrine, Smoky Quartz, and Rock Crystal. The color of Amethyst specimens from certain localities slowly fade upon prolonged exposure to light. Much Citrine is artificially formed by heat-treating Amethyst. | ||||||||||||||||
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Uses | Amethyst is one of the most popular gems. It
has a beautiful color and is rather common, making it an
inexpensive, widely used gem. Most Amethyst is faceted
into jewelry cuts, and some are cut as cabochons. Large, massive chunks of Amethyst banded with Quartz is sometimes carved into
ornaments. Amethyst is also popular among mineral collectors. Small geode sections and tumbled stones are sold to amateur collectors, while more experienced collectors go for the rare prismatic crystals and giant geode sections. |
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Striking Features | Color and crystal habits | ||||||||||||||||
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Popularity (1-4) | 1 | ||||||||||||||||
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Prevalence (1-3) | 1 | ||||||||||||||||
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Demand (1-3) | 1 | ||||||||||||||||
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Distinguishing Similar Minerals |
Garnet - occurs in very different
crystals Fluorite and Apatite - much softer (4 and 5) Spinel - occurs in different crystals, harder (7½ - 8) |
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Commonly Occurs With |
Other types of Quartz | ||||||||||||||||
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Noteworthy Localities |
Tall, prismatic, well-shaped crystals are restricted to two
Mexican localities: Piedras Parado, Las Vigas, Veracruz,
and Guerro. They occur in pale crystals that are rarely
faceted, since collectors pay well for these rarities.
Most other Amethyst is massive or in drusy, stubby, pyramidal clusters. Enormous quantities of fine
Amethyst come from Minas Gerais, Brazil. Most faceted
material is from this locality. Also in Brazil is Rio
Grande do Sul, Bahaia, where it occurs with Agate. Another South American country,
Uruguay, produces uniformly colored crystals in large
geodes and pipes. Very dark and clear material comes from
the Ural Mountains in Russia. Large amounts of Amethyst
are found two African countries: Zambia and South Africa. There are two notable Canadian occurrences. One is Thunder Bay, Ontario, where specimens contain an internal coating of red Hematite. The other locality is the area of Digby, Nova Scotia, where naturally rounded, waterworn Amethyst pebbles are found on the beaches along the Bay of Fundy. In the U.S., fine Amethyst crystals can be found in Four Peaks (in the Mazatzal Mountains), Gila Co., Arizona; in the Pohndorf Mine, Jefferson Co., Montana; in the Pennoyer Mine at Redfeather Lakes, Larimer Co., Colorado; Deer Hill, Maine; and in several areas in the western portion of North Carolina. In the early 1900's, excellent Amethyst clusters were found in Paterson, Passaic Co., New Jersey, but the area is now built over by urban expansion. |
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Picture Icon Links |
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Picture Links | 1. Stubby Amethyst crystals 2. Small Amethyst crystal cluster 3. Amethyst Geode 4. Tall, prismatic Amethyst crystals 5. Grouping of Amethyst crystals 6. "Canadian Amethyst" 7. Naturally rounded Amethyst 8. Ametrine |
