# Sand: A Critical Component for Beach Volleyball Courts
## 5 Discussion  
Our research allowed us to identify the quality of sand used for the construction of courts in Wroclaw and the specialised training facility in CSC-OPC in relation to the requirements of FIVB [7]. The sand from the court in Spala (CSC-OPC, sample no. 12) is the most compliant with the standards, while in Wroclaw the best sand parameters are the AWF courts (no. 4) and Skowroni Park (no. 1). Sand from the hall in Spala is the best sorted, and most homogeneous in terms of minerals, and quartz grains are well rounded. Thanks to the uniform mineral composition, the colour of the sand is bright, and the lack of admixtures with different properties causes the skin of players to remain clean after the game. Nevertheless, even this court does not completely meet FIVB standards, containing too much fine sand. Among the examined courts in Wroclaw, the opposite trend can be seen. They usually contain too much coarse sand, which is shown by the clearest example of the court at the PWR campus (no. 3). Another problem is the insufficient roundness of the quartz grains, which has been pointed out by FIVB because of the effect of grain shape on skin abrasion [7]. Round grains account for more than 50% in only four samples, and in three samples their content is less than 30%. In the extreme case of the LGW Arena court (no. 8), angular grains make up 40% of the total, which can adversely affect players' health. Surveys indicate that this court is one of the least liked by players, possibly due to the unfavourable properties of the sand used. We found gravel grains in several of the sand samples analysed. This is very unfavourable from the point of view of comfort and at times safety of the game. The presence of gravel strongly influences the looseness of the substrate, its porosity and permeability. Courts with good substrate sorting and an average grain diameter < 400 \(\upmu\)m have more than twice lower permeability than sites where the substrate shows a skewness towards coarse fractions of sand. The 'Glinianki' court (no. 9), which does not meet standards for coarse sand and gravel and has the highest permeability of all courts (over 20 m/d) is indicated by players as being the most difficult to jump out of during play, significantly leading to low satisfaction of the game. The microscopic analysis allowed us to determine the mineral composition of sand, which is responsible for its colour. Admixtures of feldspars and amphiboles make it take on a darker, less desirable colour. This condition is influenced by the origin of the sand used in Wroclaw, which comes from mines exploiting fluvial or fluvioglacial sediments. At the same time, dune sands are not used, which because of their good sorting, monominerality, and grain size distribution in the range of 70-250 \(\upmu\)m [21] should be an ideal material for the construction of beach volleyball courts. Practice indicates that sand with the highest possible quartz content will be the best material for the construction of courts. Our analyses did not indicate that the sand samples contain large amounts of clay and silt. The amount was generally less than 0.1% of the weight of the sample. This is in contrast to our observations that moving players on courts nos.1 and 11 causes a particularly large amount of silt to be stirred up. In this case, three alternative scenarios can be assumed: (1) even a minor percentage of silt content is sufficient to produce an adverse dusting effect, (2) the quartz grains are coated with silt that separates from them by mechanical stress, and (3) the mineral composition of the sand causes the grains to disintegrate during games. Scenarios 1 and 2 seem most likely, with the first not explaining why some courts were not listed as silty in the survey, despite containing this fraction in the granulometric composition. The source of the dust is not the organic material in the sand, the content of which is extremely low in all tested samples. Secondary minerals formed on the surface of the quartz grains can be responsible for the dustiness.