24 Questions
What is the primary factor that differentiates quartz varieties?
Crystal size
What is the typical treatment process for producing citrine?
Heat treatment of amethyst
Why is smoky quartz ideal for gem carvers and sculptors?
Its large crystal size and lack of flaws
What is the characteristic of the finest amethyst color?
Strongly saturated, medium-dark to dark reddish purple
What is the main factor in grading amethyst?
Color
What is the common trade name for treated black chalcedony?
Black onyx
Which country is the largest source of commercial-quality amethyst?
Brazil
What is a common practice among collectors of agates?
Giving them descriptive names
What is the characteristic of the finest chrysoprase color?
Light to medium yellowish green
What type of quartz exhibits a bumpy appearance similar to a bunch of grapes?
Botryoidal
What is the term for a type of quartz with curved or angular bands or layers that differ in color and transparency?
Agate
What is the property of some crystals that generates an electrical charge when subjected to mechanical stress?
Piezoelectricity
What type of gem has a flat or slightly domed top and is often set in men's rings and cufflinks?
Signet
What is the term for a type of quartz that is transparent and contains eye-visible inclusions?
Sagenitic quartz
What is the term for a type of Sagenitic quartz that contains needle-like rutile inclusions?
Rutilated quartz
What is the term for a type of quartz that contains needle-like or rod-like tourmaline inclusions?
Tourmalinated quartz
What is the term for a type of cryptocrystalline quartz aggregate?
Chalcedony
What type of quartz is often characterized by its curved or angular bands or layers of different colors and transparency?
Agate
What type of quartz contains eye-visible inclusions and is often transparent?
Sagenitic quartz
Which Amethyst often a deep color even in small sizes?
Zambian
Being the one of the first gems to be fashioned, how many years has chalcedony used in jewelry?
3,000
Which Chalcedony varieties is considered to be the most valuable ?
Chrysocolla-in-Chalcedony
Treated black Chalcedony's trade name is ...?
Black Onyx
Which Chalcedony variety is sold in larger quantities than any other ?
Black Onyx
Study Notes
Quartz Varieties
- Quartz varieties differ mostly in the size of their crystals.
- Many gem-quality quartz varieties are routinely heated, bleached, or dyed.
Citrine
- The finest citrine color is a saturated yellow to reddish orange, free of brownish tints.
- Most citrine on the market is produced by heat treatment of amethyst.
Chalcedony
- The gem trade considers chalcedony a separate species from large-crystal quartz varieties.
- Chalcedony has been used in jewelry for almost 3,000 years.
- Treated black chalcedony—known in the trade as black onyx—is sold in larger quantities than any other chalcedony variety.
Amethyst
- One of the most popular colored gemstones due to its wide availability, affordable price, and attractive color.
- Varied color distribution within amethyst rough yields fashioned gems in a wide variety of tones and saturations.
- The finest amethysts are a strongly saturated, medium-dark to dark reddish purple or purple, with no visible color zoning.
- Amethyst is sold in a variety of grades based mainly on color.
Chrysoprase
- The finest chrysoprase color is a light to medium yellowish green.
Smoky Quartz
- Smoky quartz crystals are often large, inexpensive, and free from flaws, making them ideal for gem carvers and sculptors.
Other Key Terms
- Agate: Chalcedony with curved or angular bands or layers that differ in color and transparency.
- Sagenitic quartz: Transparent quartz, usually rock crystal, that contains eye-visible inclusions.
- Botryoidal: A crystal growth habit with a bumpy appearance similar to a bunch of grapes.
- Signet: A tablet-cut gem with a flat or slightly domed top and sometimes a carved design, typically set in men's rings and cufflinks.
- Piezoelectricity: A property of some crystals that causes them to generate an electrical charge when subjected to mechanical stress.
- Tourmalinated quartz: A type of sagenitic quartz containing needle-like or rod-like tourmaline inclusions.
- Rutilated quartz: A type of sagenitic quartz containing needle-like rutile inclusions.
Learn about the characteristics of quartz and chalcedony gemstones, including their crystal size, color, and treatment processes.
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