Rev. Rul. 54-443

The term "quartzite," for purposes of section 114(b)(4)(A)(iii) of the Internal Revenue Code of 1939 (as amended by section 319 of the Revenue Act of 1951) and section 39.23(m)-5(a) of Regulations 118, includes any quartz rock of sufficient purity and such physical characteristics that it is used or sold for use as a refractory. It also includes any metamorphosed or silica-cemented sandstone which has a free silicon dioxide content of at least 95 percent, is so firmly cemented that it tends to break across rather than around the original sand grains, has low porosity, and is used or sold for purposes for which it is peculiarly adapted by reason of its chemical composition and physical characteristics. For example, it is used for construction and lining of industrial furnaces and in special chemical ware and apparatus because it is very resistant to high temperatures, sudden changes in temperature, and most chemical reagents. It does not include any rock which is used or sold for use as "stone," as defined in section 39.23(m)-5(b) of Regulations 118 for the purpose of section 114(b)(4)(A)(i) of the Code of 1939.