cristobalite


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cristobalite

[kri′stō·bə‚līt]
(mineralogy)
SiO2 A silicate mineral that is a high-temperature form of quartz; stable above 1470°C; crystallizes in the tetragonal system at low temperatures and the isometric system at high temperatures.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Sample Principal Secondary Trace (<5%) phase (>50%) phase (10-40%) Huayacocotla H-RMC-4 An Kln -- H-RMC-9 Cr Kln Mag H-RMC-14 Cr Kln Qz H-RMC-21 An Kln Mag H-RMC-32 An Qz -- H-RMC-35 Kln Qz -- Alumbres A-RMC-25 Qz Py Ill A-RMC-26 Qz Py Kln, Ill A-RMC-40 An Dck Cr, Ill, Sil A-RMC-45 An Dck Qz, An = andalusite, Cr = cristobalite, Qz = quartz, Kln = kaolinite, Dck = dickite, Py = pyrite, Mag = magnetite, 1ll = illite, Sil = sillimanite.
Phonolite sills Cavities Sill Dikes* Lime Mineral Quarry Upper Lower Rock Cavities Rock stone Aegirine R R Albite C VC C Almandine VR VR Amphibole group C VC Analcime C R VC VR R Anatase VR VR VR VR Ankerite C C R Apatite group VR R VR R Baddeleyite VR ER VR Barite C R C VR Bastnasite series ER ER Biotite group VR ER VR C Brookite R R R Calcite VC VC VC C R VC Celestine C R VC VR Cerussite ER ER Chromite ER ER Cristobalite R R VR Crocoite ER ER Cryolite R R R Dachiardite-Na ER ER ER Dawsonite VC VC VC VC VR Dickite ER ER Dolomite R VR R R C Doyleite VR VR VR Dresserite C C Elpidite VR VR Fluorite VC C VC ER R Franconite ER ER Galena R R R Garronite-like m.
Laboratory experiments indicate that cristobalite can be more toxic than quartz, a known cause of silicosis in workers with long-term exposure to silica dusts, but the reason for cristobalite's increased toxicity is not known, says Sparks.
Figure 7 indicates that the XRD patterns of porous alumina ceramics samples sintered at 1600[degrees]C for 2 hrs with different ratios of rice husk ash have different peaks, which refer to some of the ceramic phases including corundum ([Al.sub.2][O.sub.3]) (JCPDS file number 01-075-0785), cristobalite (Si[O.sub.2]) (JCPDS file number 00-001-0424), mullite (3[Al.sub.2][O.sub.3]-2Si[O.sub.2]) (JCPDS file number 00-006-0259), and sillimanite ([Al.sub.2]Si[O.sub.5]) (JCPDS file number 01-088-0890).
This phase consists of the change from beta quartz to beta cristobalite and is associated with a volume change up to 14.7% occurring around 2,678F (1,470C).
The DTA curves show the endothermic and exothermic reactions in a kaolinite sample during heating, such as desorption of surface water ([H.sub.2]O), dehydroxilation (structural OH-groups) and the transformation to mullite and cristobalite (Foldvari, 1997; Hatakeyama and Liu, 1998; Guggenheim and Koster van Groos, 2001).
Associated minerals are: hematite, cassiterite, quartz, tridymite, cristobalite, opal, calcite, "zeolites," mimetite and unidentified clay minerals.
CL--natural clinoptilolite-rich tuff from the Nizny Hrabovec deposit, Slovak Republic contained mostly clinoptilolite (60-80 %), and less amount of muscovite and cristobalite.
Above this temperature, cristobalite will form, depending on time temperature and particle size of the flours and grains.
As far as WSA sample is concerned, it possesses a large amorphous portion accompanied by minor traces of quartz and cristobalite. Furthermore, traces of kyanite were also found.
Amorphous silica with cristobalite, mostly in organic remains, are the major solid constituents of the Waikato.