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Chemical Formula | SiO2 |
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Composition | Silicon dioxide |
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Color | Colorless to white |
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Streak | White |
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Hardness | 7 |
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Crystal Forms and Aggregates |
There is scientific controversy whether
Tridymite crystallizes in the monoclinic or orthorhombic crystal system. Whatever the case,
it is a always a pseudomorph after Beta Tridymite, which
crystallizes in the hexagonal system, and thus Tridymite occurs in hexagonally shaped crystals. (See The crystal structure of SiO2) Crystals are usually small, and appear as thin tabular plates. They commonly form intergrowths of three individuals, forming unusual and peculiar examples. Tridymite also occurs as small grains. |
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Transparency | Transparent to translucent |
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Specific Gravity | 2.3 |
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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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Polymorphs | See Polymorphs of SiO2 |
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In Group | Silicates ; Tectosilicates ; Silica group May be classified as an oxide by a few abstract references (Oxide ; Simple oxides) |
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All About | Most Tridymite specimens are really Quartz pseudomorphs after Tridymite. Only a few
Tridymite specimens do not alter to Quartz. After Quartz replaces the
Tridymite, it retains the original, distinct crystal form
of Tridymite. There is no way to tell apart Quartz
pseudomorphs of Tridymite from true Tridymite without
x-ray analysis (which analyzes the atomical structure). The name "Tridymite" was derived from its most common crystal habit as pseudohexagonal trillings. |
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Uses | Tridymite is a valuable mineral to
collectors. Specimens of this rare and distinctive
mineral provide great interest to all hobbyists.
Tridymite is also used in scientific study. Its crystals
provide key information to how crystals form, and how
they change over in different environments. Tridymite is also synthetically produced for the production of refractory ceramics. |
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Striking Features | Unusual crystals and occurences |
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Popularity (1-4) | 3 |
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Prevalence (1-3) | 3 |
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Demand (1-3) | 1 |
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Distinguishing Similar Minerals |
The unusual crystals and mode of occurrence distinguish Tridymite from all other minerals. |
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Commonly Occurs With |
Quartz, Feldspar, Olivine, Cristobalite, Hornblende |
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Noteworthy Localities |
Some of the finest examples are come from
Zovon, San Pietro, Montagna, Italy. Upon analysis, all
crystals from this locality were discovered to be Quartz pseudomorphs after Tridymite.
Other localities include Lyttleton Harbor, New Zealand;
Dinas Head, Padstow, Cornwall, England; and Cerro San
Cristobal, Pachua, Mexico. In the U.S., Tridymite occurs in the San Juan Mountains in Colorado; Obsidian Cliff in Yellowstone National Park, Wyoming; and on Mt. Lassen in Lassen Volcanic National Park in California. |
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Picture Icon Links |
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Picture Links | Sorry. No Images currently available. |
