Depending on if evident in visual observations of the core sample (intact rock), indicate grain sizing according to Table 4-7. Grain size refers to the sizes of individual particles or mineral crystals that comprise the intact rock. Unlike soils, where grain size is generally characterized based on sieve or hydrometer tests, the grain size for intact rock is generally characterized from visual observation.

Table 4-7: Criteria for Defining Rock Grain Size

Grain Size	Description	Criteria
< 0.003 in. (< 0.075 mm)	Very Fine-Grained	Cannot be distinguished by unaided eye. Few to no mineral grains are visible with a hand lens
0.003 – 0.02 in. (0.075 – 0.425 mm)	Fine-Grained	Few crystal boundaries are visible; grains can be distinguished with difficulty by the unaided eye but can be somewhat distinguished by hand lens
0.02 – 0.8 in. (0.425 – 2 mm)	Medium-Grained	Most crystal boundaries are visible; grains distinguishable by eye and with hand lens
0.8 – 2 in. (2 – 4.75 mm)	Coarse-Grained	Crystal boundaries are visible; grains distinguishable with naked eye
2 in. (> 4.75 mm)	Very Coarse-Grained	Crystal boundaries are clearly visible; grains are distinguishable with the naked eye