BALL CLAY

Ball clay is an extremely rare mineral found in very few places around the worlds. It also is sometimes referred to as plastic clay. Ball clays are sedimentary in origin.  Ancient rivers and streams washed kaolinite (formed from decomposed granite) from its parent rock.  As the streams flowed from upland area they mixed with other clay minerals, sands, gravels and vegetation before settling in low-lying basins to form overlaying seams of ball clay.  Ball clays usually contain three dominant minerals: from 20-80% kaolinite, 10-25% mica, and 6-65% quartz.  In addition, there are other 'accessory' minerals and some carbonaceous material (derived from ancient plants) present.  The wide variation both in mineral composition and in the size of the clay particles results in different characteristics for individual clay seams within a deposit.