Most Japanese rock gardens in Kyoto have historically used gravel as one of their design elements.

Sourced from the upper reaches of the Shirakawa River it is known as Shirakawa-suna, (白川砂利, "Shirakawa-sand") despite the individual pieces being much bigger than the grains of what is regarded as normal suna (sand).

[1] This type of muted black-speckled granite which is known for its rather muted colour palette is a mix of three main minerals, white feldspar, grey quartz, and black mica which matches the aesthetic for most Japanese rock gardens.

Shirakawa-suna also has an eroded texture that alternates between jagged and smooth and is prized for its ability to hold raked grooves, with patterns lasting weeks unless weather, animals or humans intervene.

[3] Since the banning of extraction from the Shirakawa River the gravel used for both maintenance of existing gardens and the creation of new ones is sourced from quarried mountain granite of similar composition that is crushed and sieved.