Question

Which one is primary clay.

• A. Fire clay
• B. Kaolin
• C. Red clay
• D. Ball clay

Hint:

Logic Tip: Primary = Pure = Stays in Place = Kaolin. Secondary = Travels = Picks up impurities = Ball clay, Earthenware, Fire clay.

Answer 1

The Correct Option is B

Concept:
In geological terms, clays are categorized based on their geographic location relative to where their parent rock originally eroded.

Step 1:
Primary clays (also known as residual clays) are found at the exact site where they were formed. Because they have not been transported by wind, water, or glaciers, they have not picked up impurities like iron or organic matter. As a result, they are very pure, fire to a white color, have larger particle sizes, and possess low plasticity.

Step 2:
Secondary clays (sedimentary clays) have been eroded and transported far from their original source. During this journey, their particles are ground down (making them highly plastic) and they gather impurities (which lowers their melting point and alters their fired color).

Step 3:

• Fire clay: Transported, often found with coal seams. (Secondary)
• Red clay: Transported, high in iron impurities. (Secondary)
• Ball clay: Highly transported, extremely fine particle size, high plasticity, high organic content. (Secondary)
• Kaolin (China Clay): Mined directly from the weathered feldspar rock where it formed. Extremely pure and non-plastic. (Primary)

Step 4:
Since Kaolin is the classic and most widely used example of a primary clay, Option 2 is the correct answer. \[ \boxed{\text{(2) Kaolin}} \]