An investigation of the silica deposits of southern Illinois . ing. Chert, or chalcedony would, therefore, be more preferable for producing brickof this type due to their inverting directly to tridymite, while the quartz formscristobalite first and tridymite only after prolonged :- A good silica material should analyze 96% to 98^ silica ^ to ^ impurities in the form of AI2O3 and Fe203. The alkal: contentshould be below ^. The material should have a fusion point above Gone the raw state it should be hard and tough, and when crushed should breakdown in angu
An investigation of the silica deposits of southern Illinois . ing. Chert, or chalcedony would, therefore, be more preferable for producing brickof this type due to their inverting directly to tridymite, while the quartz formscristobalite first and tridymite only after prolonged :- A good silica material should analyze 96% to 98^ silica ^ to ^ impurities in the form of AI2O3 and Fe203. The alkal: contentshould be below ^. The material should have a fusion point above Gone the raw state it should be hard and tough, and when crushed should breakdown in angular fragments of various sizes. Fine grained materials are not asdesirable as those with grains of various sizes, while coarsed grained ones areusually worthless. The material should not weaken or crack upon heating, andshould show but little drop in specific gravity after one heating to Cone 15-16upon subsequent heat treatment. If possible the material should show a maximumtridymite content. cDov/ell, Page 2044. - Silica 7. PART 2. The Southern Illinois Silica. 1 Occurrence:- The silica deposits of southern Illinois are found in Union and AlexanderCounties, occurring in the Clear Creek Chert (Oriskany Division). They are inbeds of almost any thickness up to 250 feet. The origin of these deposits is atpresent not wholly accounted for, probably being a secondary deposit. The bedsoccur interbedded with limestone and green and brovm slate and shale. Thenovaculite or hard chert, comprising the greater part of the strata is at thesouthern part of the field. The deposit is close to the surface enabling openpit operation. The white silica occurs in thin bands too deep for open pit and below these bands occur the beds of gannister, and soraetimes inter-bedded with the white silica. The nature of these deposits is peculiar and nosatisfactory account of their formation can be of the Materials:- The samples of silica vary
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