The following is from the Brooklyn Botanic Garden Record, Plants & Garden 1961-62 (new series vol. 17 no. 4)
The "Sand Gardens" Of Japan
...there are centuries-old "abstract" gardens in Japan in which sand or gravel are used more frequently, because it can be raked in meaningful patterens.
In constructing the replica of the Ryoanji Temple Stone Garden at Brooklyn Botanic Garden, the gravel problem required a satisfactory solution. Washed gravel cannot satisfactorry be raked into surface patterens. Crushed gravel of uniformly-sized particles can be raked into patterens, but if it is to hold the pattern and at the same time present a satisfactory appearance (texture, light and shadow, etc.), it is necessary to combine two or three sizes of gravel particles.
After several experiments, it was found that poultry grit from the North Carolina Granite Corporation, Mt Airy, NC came closet to giving the effect obtained by the Japanese in their Ryoanji Garden in Kyoto.
Of the many size combinations we tested, one of the best proved to be:
2 parts "Grower" size
1 part "Turkey" size
1 part "Turkey Finisher"
The different sizes were thoroughly mixed, applied evenly over a flat surface, and raked into a the "wavelet" pattern.
The mixture can be recommended both for texture and holding quality. The wavelet pattern holds its form for several weeks, depending on the weather.
While mixtures with a higher percentage of small grit held the pattern very satisfactory, they were chaclky in appearance and did not resemble the orginal Ryoanji mix. --- Landon H. Winchester,
(Assistant Horticulturist, Brooklyn Botanic Garden)

I added the following:
http://www.ncgranite.com/gritmailer.pdf
grower: 3/32 - 3/16 inch (2.3813 - 4.7625 mm)
turkey: 5/16 - 7/16 inch (7.9375 - 11.1125 mm)
turkey finisher: 7/16 - 5/8 inch (11.1125 - 15-8725 mm)