What does this number measure?
A tiny mineral fragment shaped by erosion. Sand is defined by a range of grain sizes, not by a single substance. Quartz is common, but composition and colour vary with the rocks and the history of the location.
Compare the stated dimensions
The comparison uses the number in each fact sheet: altitude, height, diameter, length or distance, depending on the reference. Two values in metres do not necessarily describe the same property.
Source and limitations
Catalogue order of magnitude; a source is provided, but this measurement has not been individually audited.
Isolated grain of sand, macroscopic view.