# Sand: A Critical Component for Beach Volleyball Courts
## 2 Properties and Differentiation of Sand  
Sand is a loose sedimentary rock composed of mineral grains ranging from 0.063 to 2 mm in diameter [12]. The mineral composition of sand depends on the rock that has provided the source of the sandy material by weathering and erosion [13]. Sand is most commonly composed of quartz, which is the major component of granitic rocks. It is a very stable mineral, resistant to chemical weathering, and does not react with other substances regardless of environmental conditions. This property, combined with its high hardness (7 on the Mohs scale), means that quartz can be transported for a long time and over long distances in an aquatic or aeolian environment without changing its physical and chemical structure. In addition to quartz, feldspar grains are most common and are also abundant in magmatic rocks. Feldspars are less hard than quartz (6 on the Mohs scale) and much more sensitive to chemical weathering, making them easy to break down and transform into other minerals. Other common admixtures in the sand are mica and heavy minerals. The admixture content depends mainly on the distance from the source of the material. The resistance of quartz makes sands that are older and moved longer distances more quartz-like, homogeneous, and sorted. This makes quartz sands a more valuable material than limestone, volcanic or polymineral sands. Depending on the environment in which the mineral sediment was transported, quartz grains acquire different shapes and surface textures [14; 15; 16]. New grains formed by weathering or erosion of the bedrock have very irregular shapes, and fresh fracture surfaces are visible (Figure 2A). Grains transported by wind have a shape most similar to a sphere and a rough (matt) surface, which is the result of multiple collisions of grains in the saltation process (Figure 2B). Grains that have undergone fluvial transport are characterised by an elongated shape and a shiny surface (Figure 2C). Particularly elongated are marine (beach) grains, which align their longer axis perpendicular to sea waves. Multiple redeposition of sand can also lead to the development of various transitional forms, such as completely matted (nontransparent) grains with a shiny surface. As a principle, grains become more regular in shape as the transport and processing process is lengthened. The physical properties of sand, apart from mineral composition and grain texture, are mainly affected by the size of mineral grains. According to the Wentworth scale [17] sand is divided into very fine (0.063-0.125 mm), fine (0.125-0.250 mm), medium (0.25-0.5 mm), coarse (0.5-1 mm), and very coarse (1-2 mm). This classification can be considered universal and is commonly used in environmental studies. However, in geotechnical investigations, classes with slightly different ranges are often used which are derived from accepted standards, such as ISO 14688-1 [18], which distinguishes fine sand (>0.063 to \(\leq\)0.20 mm),  
Figure 2: Examples of grains developed under different environmental conditions. medium sand (>0.20 to \(\leq\)0.63 mm) and coarse sand (>0.63 to \(\leq\)2.0 mm). Since many national standards are used in addition to ISO standards worldwide, in this article we will identify grain size based on the Wentworth scale [17]. Very coarse, coarse, and medium sand have very high water and air permeability due to the loose grain arrangement and large voids between grains. Fine sand and very fine sand gradually increase the water holding capacity and cohesiveness of the sediment. The key factor is the contribution of silt and clay, which strongly affect the water absorption and water storage capacity by compacting the sediment. Therefore, sand containing more than 90% sandy fraction is considered loose sand [19]. The permeability of sand is also affected by its sorting. More well-sorted sands, due to the larger distances between grains, are more easily permeable than poorly sorted sediments [20]. Sediment grain size also affects the aerodynamic properties of sand.