Sand on the beach drains water well, but it also stays damp
within the tidal zone. Damp sand is firm, easy to walk on and
good for making tunnels in. |
Like most sand, green sand appears darker and brighter when wet.
Fortunately a crab, in exuming his tunnel, provided us with a pile
of grains that are damp. The picture at left also contains a bright
green leaf, for color reference, and a footprint for scale, seen
in the upper left hand corner of the image.
Sand grains are imperfect crystals, having been broken, eroded,
and scratched. These imperfections cause the light that hits them
to reflect scattered light of many different wavelengths. When wet,
the water on the crystal's surface acts to smooth those imperfections,
allowing the light to be reflected at the wavelength characteristic
to that particular mineral, in this case the green of olivine.
 A
picture of another hole, this one recently excavated by hand. The
hat is for scale.
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