Young Blonde Girl On The Sedimentary Rocks

+ Abundance of muddy matrix between sand grains
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.