Mike Humberston wrote:

I decided to look at the section on sand in Arthur Holmes's:
"Principles of Physical Geology" which used to be the physical
geologist's bible when I studied geology. Apparently there is
(or was) a British Standard which covered the size of sand
grains. For sand the appropriate sizes a

Coarse: 2 mm - 0.6 mm
Medium: 0.6 mm - 0.2 mm
Fine: 0.2 mm - 0.06 mm

To complete the picture, Gravel is:

Coarse: 60 mm - 20 mm
Medium: 20 mm - 6 mm
Fine: 6 mm - 2 mm

Pebbles are 200 mm to 60 mm and Boulders are 200 mm

At sizes smaller than that of Sand, Silt is defined as:

Coarse: 0.06 mm - 0.02 mm
Medium: 0.02 mm - 0.006 mm
Fine: 0.006 mm - 0.002 mm

Clay or Mud has particle sizes of 0.002 mm.

Thanks. I found rather similar definitions myself elsewhere yesterday.
Covers quite a range! I suppose the sand I'm thinking of in this
context (like that I was walking on near Leiden, or the stuff in my
garden shed) is 'fine' then. Although must say I'm surprised at that
lower limit of .06 mm. Unless I made a basic error, the grains I
viewed under my microscope (alongside a crude 1 mm scale) were smaller
than that.

--
Terry, West Sussex, UK