Young Blonde Girl On The Sedimentary Rocks

When sand-sized particles are deposited, the space between the sand grains either remains open or is filled with mud (silt and/or clay sized particle).
- "Clean" sandstones with open pore space (that may later be filled with cement) are called arenites
- Muddy sandstones with abundant (>10%) muddy matrix are called wackes.
Six sandstone names are possible using descriptors for grain composition (quartz-, feldspathic-, and lithic-) and amount of matrix (wacke or arenite). For example, a quartz arenite would be composed of mostly (>90%) quartz grains and have little/no clayey matrix between the grains, a lithic wacke would have abundant lithic grains (<90% quartz, remainder would have more lithics than feldspar) and abundant muddy matrix, etc.