Sand, a ubiquitous substance found in beaches and deserts alike, is more than just a grainy texture beneath our feet. It is a complex amalgamation of particles that hold the stories of their origins and the forces that shaped them. In this blog, we will delve into the fascinating world of sand, exploring its diverse sources and the unique properties that make each grain a testament to the geological wonders of our planet.
Let’s begin with a concise definition of sand. Essentially, it is any particle larger than clay or silt, yet smaller than fine gravels. However, measuring the dimensions of sand is not a straightforward task due to the uniqueness of each grain’s shape. The debate persists: should one measure the length, width, or a combination of both?
Based on my observations of the sand from the Kanon Private Nature Preserve, it becomes evident that it is a mosaic of sand grains from various locations. Multiple sources contribute to the composition of local sand.
Among the contributors are the nearshore forces, such as wave and tidal action, which erode the shoreline and sea bluffs, liberating local sand and sediment onto the beach. Natural erosion of coastal flatlands, driven by wind, water, and gravity, also adds to the local sand reserves. Notably, sand-size fragments of shells and corals from the shoreline and offshore are clearly visible, often distinguished by their pinkish, purplish, or white hues. However, it is important to note that these marine sources do not constitute the bulk of the local sand.
The primary contributor to the sand at the Kanon Private Nature Reserve is the mighty Gouritz River. As fast-moving water entrains sand particles or rolls and bounces them along the riverbed, they eventually find their way into the denser saline waters of the ocean. From there, ocean currents, wave action, and tidal forces work their magic, distributing the sand along the coastline. Meanwhile, finer clays and silts prefer to journey farther out to sea, beyond the energetic shoreline, before settling or sinking to the ocean floor (although some may not always make it that far).
The sand from the beach at the Kanon Private Nature Reserve showcases a wide range of terrigenous (land-sourced) sand grains. The grains’ various colors and opacities provide valuable insights into the minerals or combinations of minerals that constitute each individual grain. These sand grains are likely the result of the physical breakdown of diverse sources, including granitic, sedimentary, and even metamorphic rocks.
Breaking down rocks into sand-size fragments is a time-consuming process that often spans vast distances. Examining the Gouritz River and its tributaries, it is plausible that the local sand grains originate from numerous locations. Although my knowledge of South African geography is limited, a glance at a watershed map reveals that sand could have traveled from as far west as Groot, as north as Gamka, and as east as Olifants (all marked in red on the watershed map).
One day, when my kids are all grown and I have more free time, I aspire to build a grand database/catalogue of sand from all over the world. While I collect sand samples during my travels, a majority of my collection comes from friends, family, and kind strangers who bring them to me. It has become a routine request to all my acquaintances whenever they embark on a trip: “Bring me some sand.” I am grateful for their donations, and it brings me joy to hear them express gratitude for helping them appreciate the diverse array of sand types out there.
Apart from microscopic observations, I conduct various measurements on my sand samples, including dry density, angle of repose, effervescence, magnetic attraction, size, and shape. These measurements find their place on a ‘Sand Card,’ which includes details such as the location, donor, date, and a ChatGPT-generated poem about the location. Attached is a copy of the Sand Card from the Kanon Private Nature Preserve for your reference.
Let’s delve into some of the intriguing characteristics of your sand sample:
Dry Density: The average density for typical sand is 1.53 grams per cubic centimeter. However, your sand is heavier than average, making it a suitable material for ballast in old ships. While the samples I have measured so far range from as light as 0.86 g/cc to as heavy as 2.71 g/cc, your sand falls on the extreme end of the spectrum.
Angle of Repose: This term refers to the natural angle at which dry sand lies before experiencing a small or moderate avalanche. On average, sand exhibits an angle of repose of around 31 degrees from the horizontal. However, your sand boasts an angle of repose of approximately 34 degrees. This can be attributed to the somewhat angular grains and their size. Finer to medium-sized sand tends to lie at steeper angles compared to larger-sized sand, all other factors considered (such as shape, as round grains do not prefer a steep angle of repose).
Effervescence: Adding acid to sand is a geologist’s trick for determining the source of a rock or sand sample. If the sand contains carbonate or carbonate variations like dolomite, it will chemically react with the acid. Granite rock or quartz, for instance, will not react, while limestone or shell fragments will. In the case of your sand, the violent reaction indicates its composition as a beach sand, containing shell and coral fragments, as well as sand grains with carbonate or dolomite.
Magnetic Attraction: Many sands contain metals that are attracted to magnets or contain the mineral magnetite. By running a magnet through the sample, one can determine the presence and quantity of magnetically attractive sand grains. While some sands exhibit an impressive amount of magnetically attractive minerals, your sand did not have enough to note. Attached is an example of a sand with a significant presence of magnetically attractive minerals for reference.
Size: Your sand is classified as medium-grained, falling within the size range of Very Fine to Very Coarse. Attached is an image with scale details for your reference. Sands can either be uniform in size or exhibit a range of sizes. In the case of your sand, it is mostly medium-grained but lacks uniformity.
Shape: Your sand can be characterized as subangular. This suggests that the grains are composed of strong, resistant minerals like quartz and corundum. Additionally, it indicates that the sand has primarily been transported by water. Sands transported by wind, forming sand dunes, for instance, tend to be uniform in size and well-rounded due to grain-on-grain collisions during airborne transport. Water from rivers and beaches dampens collisions and somewhat protects the grains from weathering at a faster rate. Attached is a sand card featuring a sand dune sand, showcasing rounded sand grains for comparison.
In conclusion, sand is not merely a mundane substance but a testament to the geological processes that shape our planet. Each grain holds a story of its origin and the forces that brought it to its current location. The sand from the Kanon Private Nature Preserve exemplifies the diverse sources and characteristics that make sand a captivating subject of study. As I continue my sand collection endeavors, I hope to contribute to the understanding and appreciation of the myriad sand types found across the globe.
Thank you for sharing your sand sample and allowing me to explore its unique attributes. Happy sand collecting!
– Sample Research by Derek Rector
Kanon Private Nature Reserve would like to thank Zoe Merson-Davies for the idea and for forwarding us the above information, Hilton for delivering our sample to Derek Rector, who in turn provided us with the sand sample breakdown. February 2024
