Which one among the following is a mechanically formed sedimentary rock?

Sedimentary rocks are classified based on their mode of formation into mechanical, organic, and chemical categories [1]. Mechanically formed (or clastic) sedimentary rocks result from the accumulation and lithification of materials derived from the weathering and erosion of pre-existing rocks [2]. Sandstone is a primary example of a mechanically formed rock, typically composed of sand grains like quartz fragments that have been cemented together [2]. In contrast, salt rock (halite) and gypsum are classified as chemical sedimentary rocks or evaporites, formed through the precipitation of minerals from supersaturated solutions [1]. While limestone can be mechanically formed, it is more commonly categorized as an organic or chemical sedimentary rock depending on whether it originates from skeletal remains or chemical precipitation [1]. Therefore, sandstone is the most definitive example of a mechanically formed sedimentary rock among the given options.

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 13: Types of Rocks & Rock Cycle > 13.2. Sedimentary Rocks or Detrital Rocks > p. 171
2. [2] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 2: The Earth's Crust > SEDIMENTARY ROCKS > p. 19