From Coarse to Course: The Material Science of Golf Bunker Sand

This week the global sporting world again turns its eyes back to the small town of Augusta, Georgia as one of golf’s most iconic tournaments gets underway. As winter fades across the southern United States, longer days and warmer weather bring renewed energy to the region. This sense of anticipation is shared by professional and amateur golfers traveling from around the world, all competing for one of the most prestigious titles in the sport.

Beyond the competition itself, the golf course is widely admired for its carefully maintained landscape. Rolling hills, tall loblolly pines, flowering dogwood trees, vibrant azaleas, manicured fairways, smooth greens, and striking white bunkers all contribute to its reputation. Those pristine white bunkers, however, weren’t created by accident.

While the course’s plant life is studied and managed through biology and horticulture—the land was in fact once a plant nursery—the sand in the bunkers is selected with the aid of material science, mineralogy, and geology.

The sand itself isn’t native to the Augusta or the surrounding area. In fact, if you were to construct a new local course, you’d be building on top of rich kaolin clay deposits, valuable for many practical end-uses such as ceramics and additives in foods and pharmaceuticals, but not the first choice of surface on which you’d want to strike a golf ball. Instead, the sand is procured from mines in western North Carolina in the Blue Ridge Mountains. Drive due north from Augusta for about four hours and you will arrive in the small town of Spruce Pine, NC, where concentrated quartz deposits are found, having a very high purity of >99.99% SiO2. Not only is this quartz optically appealing with it’s sparkling white shine, but it also has material properties valuable to the semiconductor industry for use in common tech devices like computers, smart phones, and solar cells, among many others.

However, minerals aren’t simply extracted from the earth in a form that is easily shippable or useful to a manufacturing company. Prior to leaving the mine, the quartz is processed and milled to specific sizes. This size is critical for the performance of the quartz’s end-use application, whether it’s in electronic components or in a bunker on a golf course. How is the size measured for quality control of the milling process? While there are many particle size analysis techniques, the quartz sand is milled to sizes of approximate ranges of 1-100 micrometers in equivalent spherical diameter, the ideal size to measure using the gravitational sedimentation technique with the Micromeritics SediGraph. Why is the SediGraph the choice instrument for the mining industry and how does it work? Essentially, the SediGraph measures the settling velocity of the particles in a liquid media through x-ray absorption; by also knowing the density of the particles (which can be measured using a gas pycnometer like the Micromeritics AccuPyc) and the viscosity and density of the liquid, typically water, we can apply Stokes’ Law to calculate the particle size distribution of the minerals. To make this measurement, the SediGraph analyzes clear, particle-free water to set the “baseline” x-ray transmittance though the sample cell. When the sample is introduced, a full-scale scan is analyzed and the x-ray transmittance is lower by a certain amount due to the particles absorbing the x-rays, which means less x-rays get to the detector. As the particle settle out of the x-ray beam, more and more x-rays get to the detector. The bigger particles will settle first followed by the smaller and smaller particles. When the x-ray transmittance gets closer to the baseline, most of the particles have settled out of the x-ray beam, indicating completion of the test. The Beer-Lambert Law is used to convert the measured x-ray absorption to concentration of the particles in the liquid media.

Coincidently, Micromeritics originally developed the SediGraph to support the previously noted kaolin mining industry in Georgia, where heavy deposits of the mineral are found throughout the middle part of the state. These deposits have been mined for over 100 years, and this industry has heavily relied on the SediGraph to measure the particle size distribution of their milled clays for the last five decades. Kaolin particles are plate-like, where their geometry allows them to settle in a liquid media in a very consistent way, yielding repeatable results from multiple rounds of analysis, and thus ensuring a reliable method of testing. Prior to the development of the SediGraph, time-consuming manual methods to measure sedimentation were used. Tall cylindrical liquid columns were filled with large quantities of kaolin (or other minerals) and settling rates were monitored over time by extracting aliquots of wet kaolin, drying it, and weighing. By automating this test with the SediGraph, mining companies became more efficient and could mill minerals to more precise sizes for their customers. The popularity of the SediGraph in the mining industry spread globally and is now used to analyze various minerals like bauxite, titania, talc, barite, feldspar, silicas, carbonates, aluminas, and of course, quartz.

Circling back to professional golf: why does the particle size of the sand in a golf course bunker matter? Think about it on a broader scale. You wouldn’t want to hit a golf ball off a deposit of centimeter sized minerals like gravel, right? This would not only be difficult from a golf shot perspective but also damage the club and injure the player. Conversely, the sand shouldn’t be so fine that it can simply be blown away with the wind, leaving the course with empty bunkers, forcing players to hit off those hard kaolin or other mineral deposits. When considering the fine-tuning of sand size in the micrometer range, you want it to be just perfect so the golf ball won’t be completely buried every time it lands in the sand and the player should be able to hit the ball out with a reasonable effort. Of course, a “reasonable effort” is a relative term, where many amateur golfers struggle to hit the ball out of the bunker on their first attempt, usually resulting in a high score on the hole. Like

many things in golf, hitting a successful sand shot is all about mental acumen and physical technique. Having played the sport from a young age, I was taught early to use the “dollar bill” trick, where you envision the ball sitting in the middle of a dollar bill aligned longways towards the direction of the target (a $1 would have the ball sitting squarely on George Washington’s face as he watches you stress over the shot) and you hit the back edge of the bill, driving the club into the sand which lifts the ball, hopefully generating backspin, and landing it on the green near the hole. Too fine of sand won’t slow down the club head enough and the ball will fly over the green. Too coarse of sand will result with the club getting stuck and the ball won’t travel far enough. The perfect size sand particles will allow for consistent play and lower scores. While the specifics are certainly a trade secret between the mining companies in Spruce Pine and the course maintenance team, we know the quartz sand was milled to a specific particle size with tight quality standards, resulting in a perfect performance under elite playing conditions. If you are lucky enough to obtain tickets to attend the tournament in person to enjoy the breathtaking course and watch some fantastic golf, or if you’re simply watching at home like the majority of golf fans like myself, just remember when you see a player hole out for a birdie from a greenside bunker, that sparkling white quartz sand was carefully engineered to create that immaculate shot.