Riding Arena Design - Footing and Flooring Products
We have found it more easily comprehended by providing the following visual chart.

Issues Addressed
~ Footing Products ~
Issues addressed, Indoor Arena
Non-Silica
Sand
Prority 1: Long-Lasting Sand Type - will not degrade into stone dust
P2: "cushion" against concussive injuries
½
½
N/A
¾
P3: traction + flexibility ("bounce")
½
N/A
P4: low-maintenance riding surface - prevents surface "deadness" while retaining dampness
N/A
¾
Issues addressed, Outdoor/Covered Arena
Non-Silica
Sand
P1 / Top Priority is twofold - drainage + integrity.  This applies to all outdoor equine areas (not only riding arenas):
(A) Drainage/Separation - integrity of this investment
½
¾
(B) Mud prevention - usable 365 days / year
½
¾
Priorities applicable to riding arenas only:
Non-Silica
Sand
P1:  Long-Lasting Sand Type - will not degrade into stone dust
P3: "cushion" against concussive injuries
½
½
N/A
¾
P4: traction + flexibility ("bounce")
½
N/A
P5: low-maintenance surface - prevents surface "deadness" while retaining dampness
N/A
¾
 ______________________
  Reference: The article below provides a fairly simple explanation of the differences between:
~ silica sand (sometimes called "quartz sand" or "sea sand"),
~ and all the other types of minerals which compose naturally occuring or manmade sands.


About Silica Sand  [abridged, for full article goto >> http://egj.lib.uidaho.edu/index.php/egj/article/view/3085/3043 ]
The Time of Sands: Quartz-rich Sand Deposits as a Renewable Resource
Nelson R. Shaffer
Nannovations, USA
... Sand on the Move
Weathering and Transport
The mineral mosaics of rocks degrade and fall apart once subjected to surface conditions that mount a complicated assault of chemical and physical forces collectively known as weathering. Temperature changes, wetting and drying, sunlight, microorganisms, and most importantly freezing and thawing of ice or crystallization of other minerals produce repeated mechanical forces that force originally interlocking mineral grains apart. Chemical reactions especially those involved with water further liberate and modify mineral grains. Weathering is especially severe in high mountains. Over time high mountain ranges are virtually flattened by weathering (Ritter, 1986).

Rock and mineral fragments, once liberated from their igneous origins, move by gravity, ice, water, even air currents toward the lowest points on Earth usually the sea floor. Erosion and transport of grains result in destruction of physically weak minerals as they cascade down mountains, crash into boulders, and grind against each other. The constant jostling reduces sizes of mineral grains, grinds off corners and eliminates unstable or weaker minerals. The aggregate of weathered and transported grains are called sediments.

Sediments, like humans, reflect the rigors of their experiences. Mineral grains that have traveled far have more refined compositions, shapes, sizes, and companions. Mature sediments are those which have long experience in traveling. Silica sand deposits are usually mature or supermature. Geologists employ sophisticated measurements to characterize sediments. One of the most common is grain size which is determined by the screening process as discussed earlier. Natural deposits contain a range of shapes and grain sizes from fine (Figure 10) to coarse (Figure 11).

Particles that are immature generally are angular in shape (Figure 12), but they become more rounded with transport and maturity. Many sand consumers prefer very round grains (Figure 13) because they flow easily and react completely, but for some uses such as foundry molds, angular grains are preferred because they form a more stable body. Abrasive producers also prefer angular sands. More mature sands are well sorted meaning that they have a relatively limited size range and sedimentologists use sophisticated statistics to quantify size, angularity, and sorting of grains.

Mature sands tend to be made dominantly of one mineral, quartz. Younger sediments often contain relatively unstable minerals such as mica or feldspar or even individual rock fragments containing several different minerals. Very long travel times or multiple transport events can lead to deposits of remarkable purity. Super mature sands often are more than 95% quartz with some natural deposits containing 98% quartz. These high-purity sands have numerous economic applications and are required for glass manufacture (Table 2).

Sediments deposited by glaciers are almost never pure enough nor of proper sizes to be used as industrial sands but most can be used for construction purposes. Moving water or air are great media for sorting and refining raw sand materials . . . (abridged)