For manufacturing silica refractories we use quartzite. Now Quartzites are classified under 2 catagories- crytocrystalline and coarse crystalline. I like to know what is the range of crystal size( in micron) for cryptocrystalline quartzite.
"Cryptocrystalline" is very fine-grained, crystalline material that is incompletely resolved by the light-microscope!
There is no uniform grain size indication for the term "cryptocrystalline"!
There is no uniform grain size indication for quartzites!
Some petrographers use an upper limit of 0.004 mm (= 4 micron), others use an upper limit of grain size of discrete crystals of less than 0.001 mm (= 1 micron).
Best regards,
Guenter Grundmann
Dear Mr. Guenter,
Thank you for your kind co-operation. But in international specification for silica brick for cokeoven it is clearly indicated that cryptocrystalline and coarsecrystalline variety of quartzite has different RQ level.
Can you please suggest any literature supporting your statement?
Regards
Shubhrajyoti.
According to the Glossary of Geology the term “quartzite” has two meanings (quotation):
“quartzite [meta] A granoblastic metamorphic rock consisting mainly of quartz and formed by recrystallization of sandstone or chert by either regional or thermal metamorphism; metaquartzite.”
“quartzite [sed] A very hard but unmetamorphosed sandstone consisting chiefly of quartz gains that have been so completely and solidly cemented with secondary silica that the rock breaks across or through the grains rather than around them; an orthoquartzite. The cement grows in optical and crystallographic continuity around each quartz grain, thereby tightly interlocking the grains as the original pore spaces are filled. Skolnick (1965) believes that most sedimentary quartzites are compacted sandstones developed by pressure solution of quartz grains.”
Furthermore, there is no term "coarsecrystalline" in petrographic usage.
Instead, according to the Glossary of Geology, the term exists =>
"coarsely crystalline" Descriptive of an interlocking texture of a carbonate having a diameter of its own in the range of 0.25-1.0 mm (Folk, 1959), or exceed 0.2 mm (Carozzi & Textoris, 1967) or 4 mm ( Krynine, 1948). "
You can see that even in this case there is no uniform grain size specification.
Furthermore, the term "grain size" is differentiated into:
a) "particle size" and b) "granularity".
All in all, the definition of "grain size" and the definition of "quartzite" is not that simple!
Best regards,
Guenter Grundmann
Thank you so much for your answer!
In my question I was always asking for the crystal size of Quartzsite, never for grain size of Quartzsite.
I have another question regarding the grain size of Quartzsite... For manufacturing silica brick, if one sample is made with 3mm max grain and another sample is made with 2mm max grain size. Then according to you which brick will have low RQ and other thermo mechanical properties.
I think there is a fundamental misunderstanding here:
If you use the term "crystal size", this means the size of a subhedral or euhedral crystal with crystal faces (length x width x height). In the case of an unhedral crystal fragment, you cannot accurately determine the former, original crystal size. Attached here are two photomicrographs (with crossed polarizers) of a thin section of a metamorphic, cryptocrystalline quartzite (width of image 500 micron). The single unhedral quartz crystals (grains) show sutured grain boundaries and sub-grain boundaries. In both cases it is completely impossible to determine an exact crystal-, or grain-, or particle size here because the three-dimensional extent of each single unhedral crystal is unknown.
I ask you to show us a thin section or polished section of your quartzite, then we can discuss the possible crystal-, or grain-, or particle size of each quartz crystal as a rock forming component of the quartzite. Many thanks in advance,
Best regards,
Guenter Grundmann
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