What is a characteristic feature of shale when drilled?

Shale is a fine-grained sedimentary rock composed primarily of clay minerals and silt. When drilled, one of its characteristic features is that it exhibits thin soft flakes. This flaky texture is a result of its layered structure and the alignment of clay minerals. The layers can easily separate, making the material appear in thin sheets or flakes during the drilling process. This property can affect the drilling technique and the type of equipment used since handling flaky materials requires different considerations compared to more solid rock formations.

The other characteristics mentioned do not accurately represent the behavior of shale. For instance, shale does not typically crumble easily into small pieces nor does it produce large chips, which are more indicative of harder, more brittle rocks. Additionally, shale usually does not harden upon exposure; rather, it remains relatively soft and can even absorb water, further influencing its flaky quality.