EDUCATION CENTRE

Ball Clay or China Clay?

What is Ball Clay?

Ball clay is a rare mineral, found in very few places around the world. It is an important component in a wide range of goods which are essential in everyday life.

A good technical definition is:

"fine-grained sedimentary plastic clay in which the clay mineral Kaolinite predominates, and which has a light or white colour after firing to 1200oC under oxidising conditions."

The name "Ball Clay" dates back to the early methods of mining, when clay was dug using specialised hand tools, which extracted the clay in rough cube shapes of about 25cm each side. As the corners were knocked through handling and storage, the clay cubes became rounded and "ball" shaped.

Another early name for the clay was "Pipe Clay", because one of its earliest uses was in clay tobacco pipes. According to tradition, Sir Walter Raleigh smoked his first pipe at Cornwood in South Devon. The short clay pipes were called cutties and the Devon Pipe Clay also became known as Cutty Clay.

Today, the term "Plastic Clay" is used around the world to describe both Ball Clays and also clays with similar mineralogical properties.

What is the Difference between Ball Clay and China Clay?

The mineral kaolinite forms a major component in both ball clay and china clay (which is also known as kaolin). But the two materials are quite different from each other.

China clay (mostly composed of kaolinite, mica and quartz minerals) remained in the place where it was formed as the feldspars in the granite decomposed. In South West England, the funnel-shaped deposits of china clay remain located amidst their parent rock - the surrounding "granite matrix".

However, ball clay is a sedimentary clay - carried far from where the kaolinite was first formed. Rivers and streams washed away the decomposed granite, mixing it with other clay minerals, sands, gravels and vegetation as they flowed down from the uplands to form the deposits of ball clay in low lying basins. In ball clays, there are usually three dominant minerals: from 20 - 80% kaolinite; 10-25% mica, and 6-65% quartz. In addition, there are other 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). The wide variation in minerals make-up, and in the sizes of the clay particles result in different characteristics for individual ball clay seams.

Today in South West England, the clays are both mined in quarries, but using very different techniques.

China clays are washed from the surrounding rock using very high pressure water jets to break down the crumbly material into a slurry which is pumped away to be refined and yield high quality kaolins.