What is the correct sequence from the smallest to the largest grain of the following types of clastic rocks?

Clastic sedimentary rocks are classified primarily based on the grain size of the particles that compose them. According to geological standards, the sequence from smallest to largest grain size is clay, silt, sand, and then larger clasts like pebbles or boulders. Shale is the finest-grained rock, composed mostly of clay-sized particles [3]. Siltstone consists of slightly coarser silt-sized grains. Sandstone is formed from medium-grained sand particles, typically quartz [1]. Finally, conglomerate is the coarsest type, containing large, rounded clasts such as pebbles or cobbles exceeding 2 millimeters in diameter. Therefore, the correct ascending order of grain size is shale, siltstone, sandstone, and conglomerate [3]. This classification reflects the energy of the environment where the sediments were deposited, with finer grains settling in quiet waters and coarser grains requiring high-energy transport.

Sources

1. [3] 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. [1] https://www.usgs.gov/faqs/what-are-sedimentary-rocks