69. Which of the following substance is highly plastic ? A.Quartz B.Mica C.Granite D.Clay
Answer: Option D Solution: Clays exhibit plasticity when mixed with water in certain proportions. When dry, clay becomes firm and when fired in a kiln, permanent physical and chemical changes occur. These reactions, among other changes, cause the clay to be converted into a ceramic material. Because of these properties, clay is used for making pottery items, both utilitarian and decorative. Different types of clay, when used with different minerals and firing conditions, are used to produce earthenware, stoneware, and porcelain. Prehistoric humans discovered the useful properties of clay. Some of the earliest pottery shards recovered are from central Honshu, Japan. Clay tablets were used as the first known writing medium, inscribed with cuneiform script through the use of a blunt reed called a stylus. Purpose-made clay balls were also used as sling ammunition.
