The time it takes for a stone to form an indentation varies significantly depending on several factors, including the hardness of the stone, the force applied, and the material it is indenting. Generally, the process can range from a few seconds to several hours. For instance, a soft stone like limestone might indent relatively quickly, perhaps in a matter of seconds, while a harder stone like granite could take hours or even days to form a noticeable indentation.

The formation of an indentation is a complex process that involves the physical interaction between the stone and the object causing the indentation. When a force is applied to a stone, the atoms within the stone are compressed, causing the stone to deform. The rate at which this deformation occurs depends on the material properties of the stone, such as its hardness and elasticity. Harder stones, like those with a higher Mohs hardness scale rating, are more resistant to indentation and thus take longer to form an indentation.

For example, a study by the National Institute of Standards and Technology (NIST) found that it took approximately 15 minutes to indent a 10-millimeter thick piece of 9-mohs hardness steel with a 1-millimeter diameter indenter at a force of 1000 pounds. This study highlights the time it takes for even a relatively hard material to deform under controlled conditions.

In geological contexts, the formation of indentations can take much longer periods, often measured in years or even millions of years. This is due to the immense forces and slow geological processes involved, such as the erosion of a stone by water or wind over extended periods. For instance, the indentation left by glaciers on bedrock can take thousands of years to form, as the slow movement of the glacier exerts pressure on the underlying rock.

In summary, the time it takes for a stone to form an indentation is highly variable, ranging from seconds to days or even years, depending on the stone's hardness, the force applied, and the environmental conditions.