Quartzite GEOLOGICAL CLASSIFICATION Quartz-based stone is consolidated sand consisting chiefly of quartz grains with various types of cementing material, including quartzites, which are metamorphosed sandstones. Quartz-based stone can be further classified according to the free silica content of the stone. Sandstone contains a minimum of 60% free silica content. Quartzitic Sandstone has a minimum of 90% free silica content. Quartzite has 95% minimum free silica content. Subclassifications include bluestone, brownstone and flagstone. COLOR AND VEINING The color, veinings, clouds, mottlings and shadings in quartz-based stone are caused by substances included in minor amounts during formation. The purest quartz-based stones are nearly white. Colors are primarily due to iron oxides. The presence of limonite usually yields yellow, brown and buff shades; the presence of hematite yields darker brown or red. Oxidation of iron-bearing minerals upon exposure may cause some stone to change color after installation. TEXTURE The term "texture", as applied to quartz-based stone, means size, degree of uniformity and arrangement of constituent minerals. Quartz-based stone consists of essentially quartz; some are nearly pure quartz. Grains of quartz may be well-rounded or angular, depending upon the degree to which they were water-worn before consolidation. Some deposits show remarkable uniformity in size of grains. This grain composition can affect the texture. Texture of quartz-based stone is also affected by the way that the grains of silica fracture. Sandstone frac- tures around the constituent grains. Quartzitic sand- stone fractures around or through the constituent grains. Quartzite fractures conchoidally throughout the grains. Quartz-based stones are the most variable type of di- mension stone, due to wide variety in degree of ce- mentation and type of cementing material between the grains. There are four common cementing materials: iron oxides, clay calcite and quartz. All stages of ce- mentation are found in nature, from incoherent sand- stones that may be crumbled between the fingers to the most hardened quartzites. all types between these extremes are used commercially. Sandstones are generally more porous than other di- mension stone. Quartzites, on the other hand, can have as little pore space as granites. FINISHES Quartz-based stone surfaces may be finished in a number of ways. Typical finishes are: POLISHED FINISH A glossy surface which brings out the full color and character of the quartz-based stone. HONED FINISH A satin smooth surface with little or no gloss. SMOOTH PLANED FINISH A smooth finish, without gloss. RUBBED FINISH A smooth, flat, non-reflective surface. SAWN FINISH A comparatively rough surface. NATURAL CLEFT A cleavage face formed when the quartz-based stone is split into thin sheets. Other finishes such as machine tooled, split face or rock face are available. Some stone finishes can affect strength and durability. Examples are bush-hammered and thermal finishes which initially reduce a stone's thickness and also make it more vulnerable to weakening from exposure to freeze and thaw cycles. THICKNESS Standard thicknesses for sandstone are generally 1 1/2 inches (4cm), 2 1/4 inches (5.7cm), 2 1/2 inches (6.4cm), 3 inches (7.6cm), 31/2 inches (9cm) and 4 inches (10cm). Standard thicknesses for quartzite include 5/8 inch (16.cm), 3/4 inch (2cm), 1 1/2 inches (4cm) and 2 1/4 inches (5.7cm). Metric thicknesses given above are approximate; cutting can be made to exact metric measurements through conversion of English values to metric equivalents. Note that as quartzite-based stone is cut thinner its tensile strength is diminished.