砂

1. Origins, structure, and basic meaning

• Structure: The material noun 砂 (すな) denotes sand, fine grains formed from broken rock.
• Basic usage: Sand can 靴の中に入る, or it can be the material in 砂で山を作る.

2. Common pitfalls and similar expressions

• Granular sand
  • It is commonly treated as an uncountable material rather than one separately counted grain.