Silica cryptocrystalline

In addition to the above crystalline phases sdica also exists in a few micro-crystadine forms. Such micro crystalline or cryptocrystalline silicas occur in nature and include diatomaceous earth, flint, and chert. They are mostly of biogenic origin forming from compaction of amorphous silica over geologic time. 

Recent non-oceanic sediments where zeolites are known to form most often contain cryptocrystalline silica (Brown, et al , 1969 Heath, 1969, Moiola, 1970 Hay, 1964). 

Chert a hard, extremely dense or compact, dull to semivitreous, cryptocrystalline sedimentary rock, consisting dominantly of cryptocrystalline silica. 

Opaline/fine-grained massive Quartzitic No detrital component, massive, comprising opaline, chalcedonic or cryptocrystalline silica Grain supported fabric cemented by overgrowths on detrital quartz... 

The aim of this work is to study basalt quarries located in the NE of Argentina to identify deleterious species, mainly fresh and devitrified volcanic glass, expansive clays and residual cryptocrystalline silica. 

These rocks are suitable for use as aggregates in concrete due to their physical and mechanical properties. However, there are some engineering works where important damage has been detected as result of alkdi-silica reaction due to the presence of volcanic glass (fresh and devitrified) and cryptocrystalline silica (e.g. Shayan Quick 1988, Marfil Maiza 2001, Marfil et al. 2010). 

The alteration process causes the precipitation of clays (nontronite) and cryptocrystalline silica. The rock has undergone feldspatization, detected by the presence of intergrown anhedral sanidine. 

Nontronite, ferriferous saponite, chlorite and celadonite associated with cryptocrystalline silica (trydimite) were identified by XRD. 

Considering the petrographic characteristics of the studied rocks, the main source of soluble silica is volcanic glass and cryptocrystalline silica (tri-dymite) caused by glass alteration. The presence of expansive clays can contribute to increase the expansion values in the accelerated mortar bar test method. 

In previous works, deteriorated concretes elaborated with basaltic aggregates were studied (Maiza et al. 2010). They constitute a section of National Road 127, pavements in Curuzii Cuatia city (near the quarries) and a runway in Corrientes city. In all the concretes the aggregates used were those studied in the present work, which concluded that the major cause of deterioration was the development of ASR. The concretes showed severe cracking with development of neoformation materials (zeolites, ettringite and amorphous and/or cryptocrystalline silica). 

Caolad Flint. A form of cryptocrystalline silica occurring at Cloyne, Co. Cork,... 

MicrocrystaUine Silicas. Various microcrystalline (cryptocrystalline) materials such as flint, chert, and diatomaceous earth are found ia nature (see Diatomite). These may arise from amorphous silica, often of biogenic origin, which undergoes compaction and microcrysta11i2ation over geologic time. 

Vitreous, colourless form of free silica. Formed when quartz is heated to 870°C (1598°F). Aporous siliceous rock resulting from the decomposition of chertorsiliceous limestone. Used as a base in soap and scouring powders, in metal polishing, as a filtering agent, and in wood and paint fillers. A cryptocrystalline form of free silica. 

It would appear from the above summary of natural occurrences that quartz is the most stable form of silica at near-surface conditions but that other metastable phases, representing initially poorly organized material, predominate in the natural occurrences or newly formed silica. Experiments demonstrate the persistence of metastable amorphous or cryptocrystalline hydrated Si02 at low temperature (Kittrick, 1969 Krauskopf, 1956, 1959) and slow conversion at higher temperatures (above 100 bars) (Frondel, 1962 Heydemann, 1964 Carr and Fyfe, 1958 Mlzutanl, 1970). 

Most commonly, zeolites are found in series of sedimentary rocks which contain pyroclastic material and are formed during the devitrification of this material. If the rocks are silica-rich, the zeolite species formed seems dependent upon the bulk composition and burial depth or temperature of formation (Hay, 1966). They are most frequently accompanied by silica in an amorphous or cryptocrystalline form (opal, chalcedony). Analcite and all other compositional intermediates up to the silica-rich clinoptilolite are found in this association. The most comifton clay mineral in such tuffs is montmorillonite. Zeolites are sometimes found with glauconite (Brown, et al . 1969) or celadonite (Hay, 1966 Iijima, 1970 Read and Eisenbacher, 1974) in pelitic layers or acidic eruptive rocks... 

Next to materials of the glass-ceramics type, many varieties of chalcedony, such as agate, carneol, onyx, sardonyx, heliotrope and jasper, exhibit similar changes in hardness resulting from different consolidation of the cryptocrystalline structure of silica among mineral individuals. 

We have worked out a sufficiently precise and reliable system of consistent thermodynamic constants (Mel nik, 1972) especially for analysis of the conditions of formation of iron ores. In this work, in addition to the constants of crystalline minerals, data on the stability and thermodynamic properties of the original finely dispersed amorphous or cryptocrystalline iron, magnesium, and silica sediments were systematized for the first time. Such sediments are metastable solid phases which in nature are converted into stable crystalline minerals during diagenesis and low-rank metamor-... 

SYNS ACCUSAND amorphous quartz AMORPHOUS SILICA BORSIL P CRYPTOCRYSTALLINE QUARTZ DENKA F 90 DENKA FB 44 ... 

GS-fabric Grain supported fabric - skeletal grains (i.e. grains >30 pm diameter) constitute a self-supporting framework. Subdivided by cement type (a) optically continuous quartz overgrowths (b) chalcedonic overgrowths (c) microquartz/cryptocrystalline/opaline silica in-fill... 

The composition of pure quartz is close to 100% pure Si02 because the structure of the mineral is so compact and perfect that there is no room for silica replacement by any other element. Also, quartz is insoluble in all acids except HF, which further contributes to its purity. Quartz forms many micro- and cryptocrystalline varieties. Some of them are well-known as semiprecious stones (amethyst, citrine, agate, tiger-eye, etc.). 

A cryptocrystalline magnesite deposit was discovered in 1962 near Zarghat in the Hijaz Mountains. Although relatively pure, the deposit is small. Another crystalline, high-lime silica magnesite deposit was also discovered in 1962 at Jabal A1 Rokhan, which is located about 59 km northeast of Mahd adh Dhahab. Both of these deposits are being evaluated for possible exploitation. 

SYNONYMS amorphous quartz, amorphous silica, cryptocrystalline quartz, fused quartz, fused silica, fuselex, microcrystalline quartz, quartz, glass, quartz sand, silicon dioxide, silicone dioxide, suprasil, vitreous silica. 

Cryofluoran Cryofluorane. See 1,2-Dichlorotetrafluoroethane Cryolite. See Sodium fiuoroaluminate Cryptocrystalline quartz. See Silica, fused Cryptoxanthin. See Kryptoxanthin Crystal 78, Crystal 82. See Sodium silicate Crystal O Crystal P, Crystal Crown LP, Crystal Crown. See Castor (Ricinus communis) oil... 

CAS 60676-86-0 EINECS/ELINCS 231-545-4 Synonyms Amorphous quartz Amorphous silica Cryptocrystalline quartz Fused quartz Fused silica... 

Silica (cryptocrystalline) Chalcedony and Jasper White to black... 

Agate (syn., chalcedony) [Named after the River Achates, now Drillo in Sicily, where it was originally found] SiO, M s 60.0843 46.74 wt.% Si 53.26 wt.%0 Coordinence Si(4) (Oxides, and hydroxides) Amorphous Isotropic 6 2600 Mixture of cryptocrystalline and amorphous silica consisting mainly of chalcedony. 

Free silica (Si02) or crystalline silica occurs in three common forms in industry quartz, tridymite and cristobalite. A cryptocrystalline variety occurs in which the free silica is bound to an amorphous silica. It includes tripolite, flint and chert. Diatomite is the most common form of amorphous silica capable of producing lung disease. Some of these forms can be altered by heat to the more dangerous crystalline varieties, such as tridymite and cristobalite, both of which have an Occupational Exposure Standard (OES) only half that of quartz. ... 

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