Geology, Mineralogy, and Genesis of Selected Fireclays from Latah County, Idaho

摘要: ABSTRACT Fireclay deposits occur in Latah County, Idaho, as residual weathered products, and lacustrine sediments comprising part of the Miocene formation. The were developed upon granitic (granodioritic, gneissic) masses by surface weathering. fireclays derived dominantly from residuum to a minor extent volcanic ash. Mineral proportions clay are typically follows: kaolin minerals, 65 percent; quartz, 20 K-bearing micas, 12 montmorillonite— chlorite mixed-layer clay, trace. sedimentary fireclay range widely content, some that almost wholly others containing little material, or alternatively, those meeting minimal requirements fireclay. As content decreases deposits, there is corresponding increase less abundant components orthoclase, illite-montmorillonite, chlorite-montmorillonite. In both transported bodies minerals are, order decreasing abundance, halloysite, endellite, mineral. lake also contain seams poorly crystallized inferred have been ash because (1) it contains quantities tridymite, sanidine, glass, (2) notably more endellite allophane (amorphous relatively soluble NaOH) than present other deposits. Endellite seemingly has two separate geologic environments: an alteration product granodiorite gneiss weathering deposited altered fresh-water lake. It postulated common