Tridymite


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Related to Tridymite: cristobalite

tridymite

[′trid·ə‚mīt]
(mineralogy)
SiO2 A white or colorless crystal occurring in minute, thin, tabular crystals or scales; a high-temperature polymorph of quartz.

Tridymite

 

a mineral that is one of the crystalline polymorphs of SiO2. Such trace elements as Fe, Al, and Na are commonly found in tridymite. It crystallizes in the form of colorless or gray tabular crystals, spherical aggregates, spear-shaped twins, and, often, trillings. It is a rare mineral and is usually encountered in cavities of juvenile extrusive acidic rocks and in tuffs; it is also found in meteorites and moon rocks. As a constituent of Dinas brick, tridymite determines the refractory properties of the brick.

References in periodicals archive ?
In the mudstone, the < 5 m[micro] calcite fines are in different proportions mixed with < 5 m[micro] silica fines, usually with quartz, but in layers C and D partly also with tridymite and cristobalite, locally with more clay minerals, and, possibly, with roentgen-amorphous silica fines.
In all samples of layer D, relatively high contents of cristobalite and tridymite and also clay minerals are detected (Table, Figs.
The XRD analysis results show that the IR in layer B is composed of quartz with a small admixture of clay minerals, while in layer D it is represented by quartz, cristobalite and tridymite with a small admixture of clay minerals.
Sand additives that reduce veining defects provide liquid on the surface of the sand grain and favor formation of tridymite or cristobalite and greater expansion of the sand.
Fluxes decrease the temperature at which the silica starts to soften and provides liquid on the surface of the grains, increasing the reactivity and lowering the transition temperatures for tridymite and cristobalite.
Sand additives that provide liquid on the surface of the sand grain and favor formation of tridymite or cristobalite and greater expansion of the sand can reduce veining defects.
From Figure 1A it can be seen that raw oil shale sample contains calcite, quartz, apatite and tridymite (Si[O.
This final hold allows for the transformation from tridymite to cristobalite.
The crystallization process of opals goes through stages: first, open-volume crystals of tridymites and crystoballites are formed which are later replaced by more compact quartz.
The XrD techniques showed the presence of quartz, crystoballite and tridymites as well as the relative amorphicity/crystallinity ratio.