Tabular tridymite crystals from Ochtendung, Eifel, Germany
General
Category
Oxide mineral (or tectosilicate), quartz group
Formula (repeating unit)
SiO2
IMA symbol
Trd[1]
Strunz classification
4.DA.10
Crystal system
Orthorhombic (α-tridymite)
Crystal class
Disphenoidal (222) H–M symbol: (222)
Space group
C2221
Identification
Formula mass
60.08 g/mol
Color
Colorless, white
Crystal habit
Platy – sheet forms
Cleavage
{0001} indistinct, {1010} imperfect
Fracture
Brittle – conchoidal
Mohs scale hardness
7
Luster
Vitreous
Streak
white
Specific gravity
2.25–2.28
Optical properties
Biaxial (+), 2V = 40–86°
Refractive index
'nα=1.468–1.482 nβ=1.470–1.484 nγ=1.474–1.486
Birefringence
δ < 0.004
Pleochroism
Colorless
Other characteristics
non-radioactive, non-magnetic; fluorescent, short UV=dark red
References
[2][3]
Tridymite is a high-temperature polymorph of silica and usually occurs as minute tabular white or colorless pseudo-hexagonal crystals, or scales, in cavities in felsic volcanic rocks. Its chemical formula is SiO2. Tridymite was first described in 1868 and the type location is in Hidalgo, Mexico. The name is from the Greek tridymos for triplet as tridymite commonly occurs as twinned crystal trillings[2] (compound crystals comprising three twinned crystal components).
^ abAnthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (eds.). "Tridymite". Handbook of Mineralogy(PDF). Vol. III (Halides, Hydroxides, Oxides). Chantilly, VA, US: Mineralogical Society of America. ISBN 0-9622097-2-4. Retrieved December 5, 2011.
Tridymite is a high-temperature polymorph of silica and usually occurs as minute tabular white or colorless pseudo-hexagonal crystals, or scales, in cavities...
crystalline form, this substance can be found naturally occurring as quartz, tridymite (high-temperature form), cristobalite (high-temperature form), stishovite...
with all the members of the quartz group, which also include coesite, tridymite and stishovite. It is named after Cerro San Cristóbal in Pachuca Municipality...
appear to be closer to that of cristobalite and tridymite than to quartz. The structures of tridymite and cristobalite are closely related and can be...
taken to avoid sudden temperature changes that may damage the crystals. Tridymite and cristobalite are high-temperature polymorphs of SiO2 that occur in...
metallic cobalt and nickel and crystalline silica (quartz, cristobalite and tridymite). Usually, physical carcinogens must get inside the body (such as through...
crystalline forms of silica, SiO2. The most important forms of silica include: α-quartz, β-quartz, tridymite, cristobalite, coesite, and stishovite....
Pleochroism weak, from red-brown to green-brown Melting point 1670 °C (β tridymite) 1713 °C (β cristobalite) Solubility Insoluble at STP; 1 ppmmass at 400 °C...
of formation. The main three polymorphs are quartz, cristobalite, and tridymite. Quartz is the second most common mineral in the world (next to feldspar)...
have rims of pigeonite. The groundmass contains interstitial quartz or tridymite or cristobalite. Olivine tholeiitic basalt has augite and orthopyroxene...
extremely high pressure—stishovite, probably a pseudomorphosis after tridymite. From the article "First discovery of stishovite in an iron meteorite":...
they consist of imperfect crystals of feldspar, mixed with quartz or tridymite; similar bodies are often produced artificially in glasses that are allowed...
piezoelectric properties. When heated, crystalline AlPO4 (berlinite) converts to tridymite and cristobalite forms, and this mirrors the behaviour of silicon dioxide...
which are now classified as andesites. Quartz is rare in trachyte, but tridymite (which likewise consists of silica) is not uncommon. It is rarely in crystals...
Commonly in most felsic ignimbrites the quartz polymorphs cristobalite and tridymite are usually found within the welded tuffs and breccias. In the majority...
whereas in α-tridymite it ranges from 154–171 pm (6.1×10−9–6.7×10−9 in). The Si-O-Si bond angle also varies from 140° in α-tridymite to 144° in α-quartz...
if present, may be rimmed by either of these calcium-poor pyroxenes. Tridymite or quartz may be present in the fine-grained groundmass of tholeiitic...
a web of minute feldspars mixed with interstitial grains of quartz or tridymite; but in many dacites it is largely vitreous, while in others it is felsitic...
rhyolites, and extremely Fe-rich olivine can exist stably with quartz and tridymite. In contrast, Mg-rich olivine does not occur stably with silica minerals...
example, quartz will change into a variety of its SiO2 polymorphs, such as tridymite and cristobalite at high temperatures, and coesite at high pressures....
structure of interlocked six-member rings. This resembles the structure of tridymite, with aluminum substituting for every other silicon atom. This structure...
form of silica composed mostly of bladed crystals of cristobalite and tridymite. Much opal-CT takes the form of lepispheres, which are clusters of bladed...
present, it is converted into the polymorphs of cristobalite and / or tridymite. These polymorphs also experience temperature-induced inversions. The...
individual silicon and oxygen atoms to α-tridymite, similarly to the transition from α-quartz to β-quartz. β-tridymite slowly transforms to cubic β-cristobalite...
which form many polymorphs. Important ones include: α-quartz, β-quartz, tridymite, cristobalite, moganite, coesite, and stishovite. Classical examples of...
silicosis. Minerals associated with this include quartz, cristobalite and tridymite, which may all be present in volcanic ash. These minerals are described...
Martian and lunar meteorites, where it is presumably formed from either tridymite or cristobalite – other polymorphs of quartz – as a result of heating...
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